I am the smart guy at school and people always want my help. I don't want to be rude, but they pester me and I try to escape but I can't -- I end up spending a lot of time helping them to do a homework task that they were supposed to do themselves, so I just make things quick (as in 2-word answers or something like "It's in the worksheet we have"). 

But it doesn't end there. Say we had to make a PowerPoint presentation or something, and the guys realize I finished it but they have not. They then tell me to e-mail them and say "Oh, we'll change the fonts and some of the words...". It is not even getting caught that bothers me (they're actually good at changing things up) it's that I don't want to give it to them. 

I could just man up and say "No," but then these guys help me out when I need them (not in the same way; sometimes it's a problem or a question I can't answer I don't ask for everything and then "change it") so I don't want to rat them out. 

**How do I politely get them to stay away?**

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**EDIT:**

So someone wants a cultural tag, there it is. Also, the problem gets repeatedly when people get extended due dates, in which case I can't say "I'm not done" because I am supposed to have handed in the assignment.