I've done cash from day one too. I tell them during the interview, and my excuse is that the closest ATM that belongs to my bank is a half-hour away (which is true). I haven't had too many problems with late payments since I started charging a late fee, and parents have never complained about not having the check option. I think generally most people around here pay bills online or at the ATM, so checks are rarely used anyway.
I do notice that on Fridays (payday) most parents are at least 10-15 minutes later at pick-up than usual, and I'm guessing it's because that's when they stop at the machine
, but it's worth it!