Application of sandwich-based PBL teaching on the medical immunology workshop

Introduction: The Medical Immunology course is a basic and continuously updating medical course for medical students. As this course involves complex concepts, students are often frustrated by the amount of detailed material and find it hard to link the various knowledge points exactly and entirely. More effective and more engaging pedagogy beyond traditional didactic approaches is needed to drive students’ attention, understanding and memorizing more knowledge of medical immunology.

Methods: In this article, we illustrate how Sandwich-based PBL approach is applied in a 4-class workshop to this course and how to assess its advantages by examination scores and questionnaire.

Results: This Sandwich-based PBL approach could significantly improve students’ self-learning and critical thinking capabilities, communication skills and learning interests.

Discussion: We need to make great efforts to maximize the advantages of the approach and to extend this approach to more departments or more basic courses.

Introduction

As educational principles and methods are developing globally nowadays, many innovative teaching methods have appeared and are successfully applied to teaching multiple disciplines. The change from teacher-focused traditional didactic lecture-based teaching to student-centered self-directed learning has become popular in China. Didactic teaching is well-suited to teaching basic subjects and instructing students to focus on the content of their curriculum. For a long period, it has been the predominant method of undergraduate medical education. However, as the knowledge of medicine rapidly evolves, based on teacher-designed lectures and instructions, students are required to draw upon their existing knowledge and engage in active learning as opposed than passive learning. Self-directed learning would be a complementary approach to adequately preparing students (Wang et al., 2018).

The Medical Immunology course is a compulsory course for sophomore medical students in China that aims to provide them with a comprehensive overview of immunology and help students understand the immune system, how it protects their health, and gain insights into diseases such as tumors, inflammatory diseases, and autoimmunity. It is a basic but updated medical course for them. As our bodies have developed complex defense mechanisms against pathogens, Medical Immunology involves complex concepts and becomes a difficult discipline that many medical students dread. They are often frustrated by the amount of detailed material, and it is hard to link the various points exactly and entirely if teachers just adopt the traditional teacher-centered teaching method in class. In this case, traditional didactic approaches alone may fall short in capturing students’ attention, understanding, and memorizing more knowledge of Medical Immunology. Seeking a more effective and more charming pedagogy to lead them to learn actively is urgently needed.

In our Tongji Medical College of Huazhong University of Science and Technology, the dominant way of delivering this immunology course is still traditional lectures in a large class of 150–200 students. To stimulate students to effectively integrate the basic immunology concepts and to make these abstract concepts concrete, a four-lesson discussion workshop is set up at the end of the course. In this workshop, real-life cases are presented, and students are encouraged to practically apply their existing basic knowledge to discuss them. The large class of 150–200 students would be divided into several medium-sized classes of 20–30 students each, with only 1 faculty advisor available in each class. How can we stimulate the enthusiasm and initiative of students and achieve effective learning? It is particularly important to apply a tailored self-directed learning approach.

In self-directed learning approaches, problem-based learning (PBL) is a well-established learning method that adopts a problem-solving approach (Barrows and Tamblyn, 1980; Zhang, 2000). In the PBL, the students draw upon their existing knowledge and engage in active learning with a particular relevance to the given topics. A traditional PBL class typically involves only 9 to 10 students with 1 faculty advisor (Li et al., 2025). Each student is responsible for one assignment and has to present their final project work. This pedagogical approach engages students for a week to a whole semester to find an answer to a complex question. It goes beyond rote memorization and develops a surrounding of various problems put forward in class. And as a learner-centered instructional methodology, the PBL teaching method could enhance students’ autonomy, self-regulation ability, critical thinking, teamwork skills, and the ability to synthesize and make decisions (Atreya et al., 2025; Li, 2023). However, despite its advantages, more faculty members and more class hours are needed for PBL to be effectively implemented. Sandwich learning is a process of interspersed learning with group discussion, cross learning, and reporting to foster communication between students and students, teachers, and students, hence mobilizing students’ active learning and improving their ability of self-learning, critical thinking, and team collaboration (Cai et al., 2022; Shi et al., 2019). In this approach, the transformation of learning and activities is usually conducted in medium group settings of approximately 30 students, where the students are divided into multiple small groups. In addition, a sandwich session can be conducted by a single instructor.

To the best of our knowledge, this is the first study that introduces the sandwich-based PBL approach to the Medical Immunology curriculum. While traditional PBL and sandwich have been separately applied in medical education, their integration represents a novel pedagogical approach aimed at optimizing the balance between independent inquiry and collaborative learning. Given the class size and the number of available tutors, a hybrid of these two approaches might be the better way. Hence, this study proposed a sandwich-based PBL (SP) approach and then applied it to the immunology workshop, investigating its effects on sophomore medical students’ critical thinking, self-learning ability, and the course experience. The procedure for the overall research is shown in Figure 1.

Figure 1

Figure 1. Procedure for the overall research.

Application and practice

Participants and content

Sandwich-based PBL (SP) approach was used for sophomore medical students from 2018 to 2025 for all majors in Tongji Medical College (including clinical medicine, nursing, pharmacy, public health, and laboratory medicine). The overall male-to-female ratio in each major is approximately 1:1, except for nursing (approximately 10:1). The Medical Immunology course was conducted for sophomores at Tongji Medical College. Therefore, all participants in the SP groups were of comparable age to those in the control groups. Students of each major were randomly assigned to 3–4 classes in their first year in Tongji Medical College of HUST, except for nursing (only 1 class). Each semester, one class of approximately 30 students was randomly selected to take the sandwich-based PBL approach while the other classes were taught by other traditional approaches, including didactic lecture, team discussion, and voluntary presentation (Cai et al., 2022). The exact number of students included in 2024 May was 31, in 2024 Oct was 30, and in 2025 May was 33.

The teaching content is about how the immune system reacts and eliminates antigen.

Process

The teaching process includes three parts as follows:

Preparation before the lesson

According to the teaching content, the lesson plan is prepared before class. Recognition and elimination of the pathogen by the immune system is the pivotal part of the Medical Immunology course. Hepatitis B virus (HBV) infection is a significant global public health concern, particularly in China. Based on this, a case on how the immune system reacts and eliminates HBV was chosen.

This discussion content was assigned to students 1 week before the workshop. Students were asked to review the Immunology textbook and integrate the basic immunology concepts they had studied. Given that the course in Microbiology had not yet started at that time, students were encouraged to study the HBV-related part of the Microbiology textbook by themselves.

Lesson steps

Step one: questions-posing

It takes 180 min to complete this sandwich-based PBL workshop. At the very beginning of the lesson, students are encouraged to pose questions and express doubts according to the discussion content. After that, all these concerns would be classified into five issues by students and faculty advisors, basically including but not limited to: the life cycle of HBV, its structural biology; as exogenous/endogenous antigen, how HBV is processed by antigen presenting cells and then activates corresponding T/B lymphocytes; how the activated immune system eliminates the pathogen and causes liver damage; strategies for the development of HBV vaccines. This step takes approximately 20 min.

Step two: form a group

After the issues were classified, 10 min were used for the faculty advisor to introduce the concept of the sandwich-based PBL teaching method, its process, advisor’s tasks, and students’ assignments in detail. According to the paper code (consisting of a letter from A to E and a number from 1 to 5), which students are randomly selected at the entrance gate, they are divided into five groups with five people in each group. Additionally, unlike the standard sandwich teaching method, we also set an extra Group Q for asking questions to stimulate deeper thinking. The group allocation and their assignments are listed in Table 1.

Table 1

Table 1. Group allocations and assignments.

Step three: panel discussion

It is an innovative step that was different from traditional and standard PBL teaching methods. In this sandwich-based PBL method, a panel discussion would substitute for a single member’s self-study in PBL.

The first round of panel discussion is conducted within the number group (Groups 1 to 5). For example, A-1, B-1, C-1, D-1, and E-1 form Group 1. Similarly, A-2, B-2, C-2, D-2, and E-2 formed Group 2, and so on. After a short conversation among members, one issue is chosen by each group, but not assigned by the faculty advisor. Members in each group review the relevant knowledge they have already learned before the discussion, while the faculty advisor provides guidance for some deviated groups. This step should take 30 min for group members to reach a consensus on the answer to the issue. Members in Group Q randomly select one group to participate in the discussion.

In the following cross-discussion, a number of groups are separated, and students are teamed up according to the letters (Groups A to E). For instance, A-1, A-2, A-3, A-4, and A-5 formed Group A. B-1, B-2, B-3, B-4, and B-5 formed Group B and so on. In this way, each letter group consists of five students from different number groups who have already solved their own issues. Then, letter group members are required to share their answers for the assigned questions in turn, while other students raise further queries to drive deeper and more critical thinking. And corresponding students are encouraged to solve the queries; if not, the queries can be discussed in the latter process. Additionally, it’s notable that group Q could choose to take part in the discussion of any group to raise their own questions. This step should take 25 min.

After the cross-discussion, the number of groups are reunited. Members discuss the new queries posed by the last round of cross-discussion and are required to summarize what they have learned during the two rounds of discussion concerning the case, using mind maps, graphs, lists, diagrams, and other summarizing tools to accomplish the task. This step lasts 15 min.

Step four: presentation and reflection

After the panel discussion, one member from each number group will be selected randomly by the advisor as the representative to present what they have learned to other students. During the keynote speech, members of Group Q and other students are free to ask relevant questions. The presenters need to answer the questions by themselves or with their group mates. The advisor could guide the discussion and provide help if necessary.

Step five: summary and evaluation

At last, the advisor gives feedback about the teaching content. It is approximately 10 min. In this stage, the advisor evaluates every students’ performance constructively, points out the advantages and disadvantages of the discussion in this course, summarizes all relevant knowledge involved, and re-emphasizes key points, giving students a more profound comprehension of HBV, hepatitis B, the immune system of human beings and the development of vaccines. Until now, the sandwich-based PBL teaching for 180 min has finished.

Feedback after lesson

After the workshop, the final exam for the course is taken within 1 month. The exam scores among students in the same major but participating in different teaching approaches are analyzed. Furthermore, we conduct a questionnaire survey of all students who participate in the SP approach. The questionnaire consists of four parts. We intend to learn about the impact of the SP approach on self-learning ability and students’ opinions about our teaching method in part 2. Questions in part 3 are designed to measure traits in seven areas of critical thinking, including searching for the truth, open-mindedness, analytical skills, systematization ability, self-confidence in critical thinking, intellectual curiosity, and cognitive maturity. The last part is about the general situation of students’ scores in the final exam to assess students’ mastery of the knowledge points and the actual effect of our teaching method. The questionnaire is shown in Table 2. We conducted reliability and validity analyses on our questionnaire. The questionnaire demonstrated good reliability (Cronbach’s Alpha = 0.759, Cronbach’s Alpha>0.700) and good validity (the Kaiser–Meyer–Olkin measure of sampling adequacy for the questionnaire was 0.664, greater than 0.6; Bartlett’s test of sphericity was significant with a p-value of < 0.001, indicating that the questionnaire data are suitable for exploratory factor analysis, and all items passed the validity analysis).

Table 2

Table 2. Questionnaire design.

Considering that a simple questionnaire survey is not enough to learn about students’ comprehensive opinions from the bottom of their hearts, we interviewed some of the students who participated in the SP approach face-to-face to refine our research. Rather than the actual effect of our approach, the theme of face-to-face interviews is more inclined to the psychological feelings of subjects. The interview questions are designed as in Table 3.

Table 3

Table 3. Questions for a face-to-face interview.

It should be noted that data from the recent three semesters were analyzed and reported in this article.

Teaching effectiveness

The teaching effectiveness of the sandwich-based PBL approach is presented from two aspects as follows.

The exam score of students

After finishing the Medical Immunology course, students from SP and other approaches took part in the same exam at the same time. The score performance of students in this selected class was compared with all other classmates of the same major. For students majoring in nursing, due to a lack of control, only questionnaire responses were collected. Mann–Whitney U-test was applied to analyze exam results between groups. The comparison between 2022 Grade Clinical Medicine students is shown as a representative in Figures 2, 3.

Figure 2

Figure 2. Comparison of exam scores for students taking part in 2 types of teaching methods (out of 100).

Figure 3

Figure 3. Comparison of scores of related questions for students taking part in 2 types of teaching methods (out of 14).

In Figure 2, we analyzed exam scores and those of the related questions for students taking part in two types of teaching methods (U = 1502.000, p = 0.590 > 0.050). It was found that the test group (median = 86.00, average = 84.65, IQR = 10.00) had a greater proportion of students scoring over 80 than the control group (median = 88.00, average = 84.51, IQR = 13.00), suggesting that the practice of the sandwich-based PBL teaching approach did increase the share of high-performing students (typically those scoring 80 or above).

When it comes to the scores of the questions which relate to the content of the workshop (U = 1283.000, p = 0.441 > 0.050), we observed that the percentage of students who got 11–13 points in the test group (74.2% in total) was higher than that in the control group (69.3% in total). Furthermore, there was no student with a score of 5 or less (Figure 3). For median scores and average scores of the related questions, students in the test group (median = 12.00, average = 11.39, IQR = 2.00) performed better than those in the control group (median = 11.00, average = 11.08, IQR = 2.00), though their median score was a little lower than the control’s (Table 4). Therefore, we believe that the students in the test group did achieve better learning results in sandwich-based PBL pedagogy.

Table 4

Table 4. Median scores and average scores of related questions between the two groups.

Questionnaire and interview with students

Questionnaires were provided to students who participated in the sandwich-based PBL approach. We analyzed 57 valid questionnaire responses, and the evaluation dimensions and results of the survey are shown in Figure 4.

Figure 4

Figure 4. Evaluation dimensions and results of the survey in the test group.

When the semester was over, we interviewed some of the students who participated in the SP approach face-to-face. To our surprise, this approach made a deep impression on all of them. Using qualitative content analysis, we summarized the interviews into the following five topics: personal progress in studies, teammates’ motivation, emotional value, limitations of the SP approach, and suggestions for the course.

The SP approach, to a certain extent, enhanced students’ abilities in knowledge integration and comprehension.

“The panel discussion gives them a more profound understanding of the topic when discussing with others and sharing materials, helps them learn better learning skills.”

“Group discussions have honed my ability to summarize knowledge, and I am also able to pose more problems during these discussions, which allows me to further improve myself.”

Due to the second cross-discussion, the participation of group members in the discussion has significantly improved.

“Everyone needs to get well prepared, even those who were reluctant to take part in had to discuss.”

The format of group discussions in the SP approach also brought positive emotional feedback to the participants.

“When discussing the topic, I enjoy the feeling of thinking and the process of getting closer to the answer.”

They also suggested that the SP approach focused on a restricted topic, which could help them repeat the learned knowledge to improve memory and understanding. The presentation part gave them a chance to express their ideas using their own words, which was more understandable by other students and deepened their comprehension further.

However, half of the participants thought that the quality of the discussion was largely influenced by how heated it was.

“When most members of a group don’t take the discussion seriously or don’t prepare well, the ideas would be exchanged by only a few.”

And one interviewee complained that he tried his best, but when sharing his opinion and making a presentation on the platform, he was still very nervous due to the insufficient discussion in his group. When being asked what kind of role the advisor was supposed to play in the session, most of them suggested that the teacher should provide more guidance about the key points. Voluntary presenters would be better than those who were randomly picked by the advisor, because a slacker would ruin the enjoyment of brainstorming.

Discussion

The teaching of Medical Immunology, a discipline characterized by its complexity and intricate connections, demands pedagogical approaches that move beyond passive knowledge transmission. The PBL-based curriculum is more effective in promoting clinical competence; however, its efficacy in promoting a theoretical knowledge base has been questioned, and some studies have even reported deficiencies in the knowledge base in the PBL student subgroups (Zhang and Hu, 2024; Zhou et al., 2023). We propose a sandwich-based PBL approach, which not only combines the PBL and sandwich teaching methods but also takes the grouping advantage of the sandwich method, uniting groups of students to concentrate on different topics to come to their own conclusions. A primary challenge in traditional PBL is that the topic is usually too complicated for students. It would cost them too much time to get well-prepared for the whole content, resulting in a passive or perfunctory attitude toward PBL preparation. Unlike PBL, our SP approach can directly mitigate the issue. The first-round “number group” discussion could decompose the task into smaller, manageable sub-topics, effectively reducing the burden on the students. Hence, they could focus on a single theme, helping them to better master their own part before confronting the entire problem. In the next round of discussion, the students share what they have learned within the “letter group.” Unlike traditional PBL, where knowledge integration can be exhausting and complicated, the SP model makes it easier and more understandable. Each student, acting as the “expert” for their topic, is required to teach their peers. Returning to the initial “number group” gives the students a chance to revisit their original topic, correct misconceptions identified during the cross-discussion, and deepen their understanding. Unlike a traditional sandwich, our SP method includes an extra presentation part. All members of the same “number group” are united as one to present their answers. This act of teaching is a potent form of active learning, forcing knowledge retrieval and re-articulation. The process of raising questions with others, reasoning, and debating with each other can deepen students’ understanding and build a complete and logical knowledge system. Hence, our design could not only help the students to work with others and integrate the knowledge by themselves throughout the process but also enhance their class engagement and responsibility for the class.

Multiple rounds of discussion can repeatedly enhance memory. As a learner-centered instructional methodology, one of the main ideas of the approach is to let students learn the project by themselves and share knowledge with each other. Exam grades, questionnaire surveys, and interview results indicate that the SP approach could exercise students’ autonomy, self-regulation ability, critical thinking, teamwork skills, and the ability to synthesize and make decisions through group discussion and presentation. This result is broadly consistent with Cai’s and Peng’s research conclusions (Cai et al., 2022). We encourage students to think and learn independently and share in groups during the whole process.

Compared to Western learners, most Chinese students are more reserved or shier in public, especially when making speeches in front of others, due to our traditional culture. It is of value to let students show themselves in class. Our sandwich-based PBL approach does provide help for them to overcome their fear of public speaking, through randomly picking students to make presentations, discuss, and share opinions with others. Furthermore, the randomized grouping way and re-grouping step give students a chance to connect with familiar or unfamiliar classmates, making them discuss with new teammates, which could deepen their friendship with each other while benefiting from understanding the knowledge by exchanging conclusions. Making presentations in front of classmates is another way to practice their ability to express themselves.

A good advisor is also very important in the process. Before the workshop, they need to write the teaching plan carefully, develop attractive topics, and provide general information so the students can get a clear learning direction. During the discussion, mentors need to organize three rounds of discussion, listen to the discussion to understand students’ difficulties timely manner, and make a preliminary assessment for team activities. During the presentation, they also have to listen to the students’ speech carefully and make comments timely and elaborately. Finally, advisors would make a summary and offer an analysis for unresolved questions. Most importantly, they need to transfer their role from knowledge transmitter to companion or instructor. All of the processes above need instructors to engage deeply and help students stay on the right track, which is a major challenge to the teacher’s ability to manage the classroom and provide guidance.

However, there are some limitations to this approach. Most of the time, the number of students could not meet the exact number that a traditional sandwich teaching method requires, say, square numbers such as 25 or 36. To solve the problem, we created a Q group. Q members are short for question, and their duty is to ask questions during the whole process. Although they can ask questions at any time, they cannot join the discussion thoroughly like the members in other groups, failing to help other students think more actively and solve the problem better. Second, there is no appropriate way to quantify the basic learning capabilities of the students before and after the sandwich-based PBL approach. It is hard for us to evaluate how the method influences them. The final examination scores do not show a significant difference between students taking different types of teaching methods, although the questionnaire survey and interview results suggest that students improve their thinking ability, communication skills, study interests, and so on. Furthermore, the discussion workshop is set for only one time, making it hard to fully understand the influence of the approach on the students. Then, lack of enthusiasm for the discussion is another issue. We found that several students treated the course casually, staying silent during the discussion and trying to avoid the presentation, which makes it hard for the process to continue. As for this problem, it would be better for the advisor to observe students’ status, understand their difficulties in a timely manner, and make a substitution promptly.

In summary, this sandwich-based PBL approach evidently improves students’ self-learning and critical thinking capabilities, communication skills, and learning interests. We need to make great efforts to maximize the advantages of the approach and to extend this approach to more departments or more basic courses.

Data availability statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics statement

Ethical approval was not required for the studies involving humans. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

Author contributions

CH: Writing – original draft. YC: Writing – original draft. FZ: Writing – review & editing. PL: Writing – review & editing.

Funding

The author(s) declare that financial support was received for this work and/or its publication. This study was supported by grants from the Huazhong University of Science and Technology on the Construction of Teaching Teams for Graduate Courses (nos. 202317 and 202219).

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Correction note

A correction has been made to this article. Details can be found at: 10.3389/feduc.2026.1794965.

Generative AI statement

The author(s) declared that Generative AI was not used in the creation of this manuscript.

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