1. to collect something, such as homework, so that you can assess it.
2. to pay attention to something so that you are able to understand, remember or assess it. (This phrasal verb has more than one meaning)
E.g.1. Will you take the homework in or will we mark it in class?
E.g.2. It was a difficult concept, but the students seemed to be taking it in.
Both these phrasal verbs can be separated.