It is common for faculty and graduate students to conduct human subjects research on undergraduate students. Typically precautions are made to ensure that faculty do not use the teacher/student relationship to harm students. For example, the faculty member may be required to finalise their grades before they find out which students consented to participate in the research. This prevents the faculty member from incentivising students to participate by changing their grades.
Let's suppose that the researcher is an undergraduate student instead of a faculty member. Are there risks associated with the student-student relationship? Let's suppose it is a small university where students often know each other.