I have also had some problems with the IF-AT sheets, but discovered 
something that has been helpful.  Most of my sheets have been taken out of 
the plastic and stored in a manila envelope.  The sheet that has been on top 
is almost always impossible for scratch off.  When I pull the sheets from the 
middle of the stack, they scratch off with little to no problems.  

I think that as the sheets age, they dry out and then the problems with 
scratching off to reveal answers occurs.  I am more careful to keep the 
sheets stored in their plastic wrap where they are less likely to dry out.

Staci Johnson
Southern Wesleyan University