No, he signed, as everybody does, a form called STM 2, acknowledgement of terms and conditions. When the current one is not cancelled as it should be, Immigration can charge 500 Thb overstay with a maximum of 20.000 Thb when he applies for a new Extension somewhere in the future.
As you are a long time living in Bangkok, I guess you did visit the Immigration Office and applied for and got issued a big stamp with the text:
Extension of Stay is permitted up to ../../.., this is NOT a visa.
You need to cancel this Extension of Stay with documents from your school on the last day of study and leave the country before midnight. No left days possible.
And before each and everybody of the 44.000 members going to share their own experience to enter Thailand, I close it down.
There is no limit on Visa Exempt Entries, Visa on Arrival, bilateral agreements or even on Tourist visa.
There is no minimum time people have to stay abroad.
But there is common sense, not everybody wins the lotery every two months to provide him/her self with a luxury live in Thailand. Most people do have to work to gain income.
Get the correct visa, apply for Extension of Stay and all the jumping around is over and you are legally in the country.
If you already visited the Immigration Office for the Extension of Stay, you cancel your work permit and cancel this Extension of Stay at the Immigration Office. You apply for a new Extension of Stay if you can meet any requirements, if you can not meet those, your application will be not approved and you get 7 days to leave the Kingdom.
If you still during the first 90 days you got on entry, you can stay until the Admitted until date and than OR have to apply for an Extension of Stay if you can meet any requirements, OR leave the country.