Reciprocity is a potential issue in college teaching if professors benefit students in return for better student evaluation results. The reciprocity in college teaching is framed as kind intention and consequence, including teaching styles, attendance requirement, delivery mode, grading and course difficulty. This study explored whether and to what extent reciprocity exists in these forms. A dataset containing 9,543,998 records on 919,750 professors from ratemyprofessor.com was used. The results show that reciprocity exists in the five forms to different extents. The reciprocity in attendance requirement and delivery mode is relatively minor. We suggest that the reciprocity in teaching styles is instrumental to the transformation from the teacher-centred approach to the student-centered approach, that professors need not feel pressured to change courses into attendance-flexible or in-person courses, and that the reciprocity in grading and course difficulty may cause goal displacement and impair teaching effectiveness.