This email is brief and to the point, more of a final warning than anything else. Feel free to adjust if you do not have a waiting list and you feel disingenuous referring to one.
(You may also like to follow up with a call at this stage if you collected their phone number.)
Still interested in piano lessons?
Hope you’re well! Just checking in one more time about lessons for [CHILD NAME]. Please reply to this email ASAP if you still want that spot in the schedule, otherwise I’ll pass it on to the next person on the waiting list tomorrow.