We just renewed my husband's passport in June. The Bangkok embassy wanted a Thai bank draft for 100 baht included for the return envelope...not sure if there is another way.
I used to live and work in Ayutthaya as a teacher. You can request to join Ayutthaya Expats or PM me if you want other contacts for teaching there. I can't speak for getting a visa right now with all the COVID nonsense.
I understand that. When we first applied for his current visa, there were 14 documents required from the school including tax documents from the revenue service. I need a list of the required documents for renewal to give to my employer so they can gather the documents for me.
Although, it could also mean the school license, copy of the director of the school's license, or things like that. Best to ask immigration what specific supporting documents they want.
The school needs to write a letter verifying that your child is a student there and any other documentation (enrollment, report cards, etc.) to verify that he attends the school.