Multi-Grade Class - HELP!!!

I am an alternative school teacher responsible for students in grades 7 all the way up to grade 12.  I have different levels of math (Math 7 & 8 up to Algebra 2). How do I add those different students to DIFFERENT subjects (Algebra 2, Math 8th, etc.) under my 1 screen name? Right now I think I have the students (1 11th grader, 1 9th grader, and 2 8th graders) under my screen name, but they are all under Math 8.  The 11th grader needs to be in Algebra 2 and the 9th grader is different then the 8th graders.

HELP!!!! My undergrad is English and I am NOT a math person, so Khan Academy is going to be my lifesaver!