Row Level Dax

Thank you for the links, I kind of have gone through them a few million times by now and have not been able to come up with a proper solution to my question. Also, I am kind of in a deadline that I need to meet. I have a kind of tricky situation. I feel like the solution should be pretty easy and I am not looking at it in the correct order.  I am going to start explaining from the beginning. 
I have a table that contains the general student information. 

I am trying to create row level security for teachers and principals(Teachers being level 1 and Principals Level 2). The teachers should have access to see information to only the student they have in their class whereas the principal should have access to all the students within the school. 

My teachers table looks somewhat like this, 

And, the table above is the only table that has the teacher and students with their IDs on the same table. 
I have a directory table as below, 

I have tried all kinds of different scenarios but there I have not been able to come up with a proper solution to create RLS for them so I am providing a sample of the tables as they are here to see if there is a way around. I have tried creating bridge tables and calling them by USERPRINCIPALNAME and Level but have not been able to find a way to limit the teachers from accessing all the student's records.. I have a deadline coming up and any help would be very much appreciated.