I am in desperate need for help!

I have two forms, one form to which you can view students and their grades/qualified. other form is to input the data for the students scores, completed date etc for each assignment. each course is made up of 2 assignments.

I need a way or a function to differenciate the grades from the years. IF i input for ex. Jane Smith did assignment 1 and 2 in 2011 and got a total of 100%, and she got a total of 80% for the same assignments in 2012, the form needs to know NOT to add the 2012 grade into the 2011 grade. right now the total grade for 2011 is 180% as well as 2012. Does that make sense?