He's right- LT has never had the capability of DIRECTLY running LISP routines. Your instructor isn't really at fault,though (even though the institution might be).
1. Search the web for ACAD-LT utilities. There are a number of companies that sell LISP activators you run on top of ACAD-LT, and the best even have versions for ACAD-200X. You need to CALL THEM to discuss your needs, but you should find success without purchasing an upgrade to full ACAD.
2. If you can afford it, GET FULL ACAD. There are many capabilities that you won't discover you "need" until you have them in front of you. Otherwise, look for those add-on program sites.
3. As to your instructor, quite often a drafting teacher is given a copy of the CAD program they're going to teach from, and told to "learn it" before next semester. If your instructor did a fair job with "Intro to CAD" or some such, then you got what you paid for. It's a sad reality that many institutions don't have the budget to really do this job well, but at least be glad that they bought ACAD-LT instead of some less expensive alternative "CAD" program to teach from. As you've discovered, a good intro to ACAD (even -LT) is MARKETABLE.
4. Actively learn your tool, and soon you'll be ANSWERING CAD forum questions instead of asking them!
Good Luck!
C.F.