The domain model would look something like this

The student belongs to 0 or more classrooms (class can’t be used as this is a reserved word). A teacher can belong to 0 or more classrooms. Via the classroom object the teacher can reach the student of the class as both a related to the same record. However just adding the associations is not the whole story, When creating a page with a dataview you can nest a datagrid with the classes over association to allow classes to be added to the teacher. The same is true for the students. The to show the students to the teacher yoou can use the listen to widget option for another dataview that uses the data from the datagrid to display the class and inside that dataview you can display a grid with the students over association from the class. A similar solution can be used for the students and the class data.

Still not the complete story though, because you will need to setup entity access xpath restrictions to make sure the data is secure.

I hope this provides you with some more ideas on how to achieve you solution and I suggest looking at the documentation and/or learning paths on page building, domain modelling and entity access restrictions to create a robust solution.