ส้อม vs. ซ่อม
They are homophones, the same pronunciation but different meaning.
ส้อม//sôrm means a fork (type of kitchen utensil)
ซ่อม//sôrm means to to fix, to repair. In the school context, it means the second test that you have to take if you do not manage to pass the first one. However no matter how many marks you get from this second test, your grade will always be just enough to pass.
Credit pic: 9gag Thailand