I feel sorry for you and the child. Originally our half-Thai daughter went to Thai schools and at each there were problems (for me and learning) so we kept changing to "better" schools. But each had its own problems including one which immediately after we joined there, they rid themself of all the farang teachers and even used our daughter on their advertising brochure. We immediately left there, joined another which was a 12-year plus the Kindergarten, daughter started at 3rd grade. By the second year, the school dropped grades 7-12 and added more kindergarten as they got more funds for that (extra teachers per each classroom) but the school then had a 2-year waiting list to get into it. I argued with the teachers and owner about the extremely poor English lessons to the point that we dropped out of that school too and moved to CM from BKK. At CM we got into a brand new school, just opened, expensive but with a good reputation of the parent university
and the school was on the physical scale of any US high school. However, poor management meant poor instructions and we decided to leave although offered a full scholarship to remain another year. But by the 3rd year of it open, almost every student over Kindergarten had left as did most of the farang teachers. So, daughter tested at several of the better reputation schools in CM and we opted for Chiang Mai International School with daughter starting 6th grade. By graduation, daughter speaks, reads, writes, and teaches Thai, English, Chinese and Korean. She taught Chinese at a different high school, worked as the Chinese teacher's aide during her junior year, was selected as the best Chinese student for the entire school, passed the level 4
Korean international language test given by the Korean govt each year (many college-level students cannot pass other than level 3). She is currently going to the number one university in Thailand (I realize that standards may not meet developed countries but this is a liberal arts program) learning Japanese language and international culture for a double degree. CMIS has great teachers and programs for all their students whether they will go on to international studies or what ever. At first, our daughter was bored with most of the schools but I never heard any complaint from her about CMIS and their curriculum. Every move was discussed with my Thai wife who agreed wholeheartedly with EVERY move! Best wishes for your daughter.