[plt-scheme] awkwardness in automarking

My TAs, who run scripted automarking tests on submitted student code, 
report that students using early HtDP language levels (say, Beginner) 
occasionally use identifiers, such as "time", that have meaning in 
higher language levels. The TAs were running their tests in Advanced by 
using "load" (I think -- I haven't looked at what they're doing in 
detail) and the student code was failing because of redefining "time", 
whereas it would have run in Beginner. I suggested going to Pretty Big, 
but the syntax of define-struct is different, and tests again seem to 
break. Is there an elegant solution to this? Thanks. --PR