Calling all math guys/girls

[egodog48]

Basically I need a formula to compare the student grades of two individual classes against each other. In other words, is one class performing better than the other one and to try and compare the individual students to each other if possible. I am only using the final semester letter grades, but will be assigning a value to the letter grades (A=4,B=3, etc.) ANyone, please help. Im not so good with statistics. Im sure its an easy formula but I need variances and coeeficients and stuff if you can help let me know.