Originally Posted by SunshineMama:
If it were me I would just take the check, and remind him that from now on you must be paid in cash only (uness payment by check will cause a probem for you when you cash it- then give it back at pick up and tell him you were caught off guard this morning and can ony accept cash). Sorry! I hate when parents do stuff ike that 
Ditto. Just be honest with him and tell him how you were caught off guard because not a SINGLE parent has ever paid you in the wrong form and you honestly were thrown off by it. Tell him he needs to pay in cash. Honestly, I'd give him a courtesy text or call before pick-up (anytime today really) and tell him to bring cash when he comes. That way he has the chance to go to an atm. You can return the check then.