I have a problem. I have a list about some pupils and I have already linked them another tables as you told me (Because they are in different classes). But now I need to sort these pupils in the main table by their grades. If I do this, it will also effect to another tables, and there would be wrong information. So my question is that can I link by pupil's names? Thank you for your help in advance!

Yes, you can use the function VLOOKUP to look up a pupil's name in a table and bring back adjacent data about that pupil.