Primary school visitor visa

Hi, my wife and her son (from the Philippines) are here on visitor visa for 12 months. It says on their visa they can only study 3 months. My wife wants him to go to a public school around the corner from us. I dont really see the point if he is only allowed for three months. My only other option is for him to do an online school I found in the Philippines but it cosst quite a bit. Does anyone know of any other options? Or does anyone have any experience with this? Is there a way to extend the three months for study?