Try looking at t-tests for this kind of thing. If you have more specific questions about this then just ask.
I have two groups of students: 1 group from low performing schools and 2nd group from high performing schools. EAch student has entered my university with a entry score of either: 260, 300, 340, 360. Each student has sat an exam at university and I want to test whether the results (e.g. 50%) are the same for both groups, that is, has a student from a low performing school who entered with a score of 260 peformed the same in the exam as a student with same entry score from a high peforming school. Which test to do? Thank you