Collaborative testing has been demonstrated the ability to improve students' performance, enhance students' learning, and aid in knowledge retention in many different courses. However, this examination mode lacks the process of teacher feedback. Herein, a short teacher feedback from was added immediately after the collaborative testing to improve the students' performance. A parasitology class of 121 undergraduates was randomized into two groups: "group A" and "group B." Collaborative testing was carried out at the end of theoretical teaching. During the test, students would first answer questions as individuals for 20 minutes. Then, students from "group A" answered the same questions in groups (5 students in each group) for 20 minutes, while the group-testing duration was only 15 minutes in "group B." Immediately after the group testing, teachers conducted a 5-minute feedback about the morphology identification according to the analysis of the answers by "group B." Four weeks later, a final test was conducted in an individual test. The total scores and scores for each examination content were analyzed. The results showed that there was no significant difference in the final exam scores between both groups (t = -1.278, P = 0.204). However, the morphological and diagnostic test results of the final examination in group B were significantly higher than those of the midterm examination, while there was no significant change in "group A" (t = 4.333, P = 0.051). The results confirmed that the teacher feedback after the collaborative testing can effectively make up for the students' knowledge gaps.