School lets out in 10 minutes and you just remembered it's picture day tomorrow! You could send an email and hope the parents read it before tomorrow morning.
You could give each student a bracelet with the reminder. Kids love showing them off and parents are sure not to miss it.
The simplest of designs for easy (and cheap) printing and non-gender specific so the boys won't mind wearing them either.
Crazy Hair Day
Show & Tell
Plus a blank Word template to create your own!