The 90-days report is a "Notification of staying in the Kingdom for more than 90 days". It is done by filling in immigration form TM47.
"An alien who has been granted permission to temporarily reside in the Kingdom, if staying in the Kingdom for more than 90 days, that alien has a duty to report his/her residence to an Immigration Bureau officer every 90 days.
This is in accordance with Section 37(5) of the Immigration Act B.E. 2522."
Also, as Andi wrote already - to be an english teacher in Thailand you must have a bachelor’s degree. That is a requierment to receive a work visa (Non-Immigrant B), which is needed to get a teaching license.
You can't "go for" either work visa or educational visa.
To get a work visa (Non-Immigrant B) you need a job first and have the necassary paperwork from the employer (plus apply for a work permit once you have the visa).
For an educational visa (Non-Immigrant ED) you must be enrolled to a school/institute/university to study in Thailand and have all the requiered paperwork from the school.
I suggest that you do some more research about different Thai visas - the web page for the Thai embassy in your home country is a good place to start.
After that, he e-mailed the embassy to ask if his financial situation could be a reason for rejection. They replied that the visa would not be approved with a sponsor.
Because of that, he contacted an agent that offered to do a new application for him, but told him that he had to wait 3 month for that.
Meanwhile he went back to Thailand, planning to apply through an agent later...
However, he never needed to use an agent. The embassy suddenly asked him to submit a new photo to his initial application and the next day it was approved (even though they had written in an e-mail that it would not be aporoved with a sponsor).