I have two datasets of teacher and student data, each representing a level in a multilevel model. The teachers have a unique link to a student taught in one specific class, and teachers have unique response items for each class. On the other hand, each student have only a single entry and do not have unique data for each class. This leads to the issue that teachers may teach the same student in more than one class, which creates a duplicated entry of the student if the datasets are merged.

I fear this may lead to bias, and have been wondering how to deal with this issue. So, I was wondering if is there a way to connect level 1 (student) data to level 2 (teacher) data without duplicating the student data? Or, alternatively, are there other workarounds?