@Emily ***********
No, once you leave you don't need to report.
When you come back, they'll stamp a new "entry" date and also give you a new TM30 slip.
You will then need to report 90 days after the new date
HOWEVER... Your landlord or whoever you have as a Thai person that is responsible for you *should* report within the first 48 hrs of you getting home (not just arriving but actually back to your home address) as this needs to be done... But I'm pretty sure it's for your landlord or school to do.