There are the elite private schools that get their students because of the universities they qualify for.
Then there are the money schools that are not in fact schools but businesses. These are run on the fact that students score high on tests and get great grades, preparing them for the next level.
The school only cares about keeping parents happy. That means Somchai is doing well in school and wants to stay at the school. Let's face it, the teachers are ok but have been told that they must have a 100% pass rate. After all, if they start failing students, the parents will pull out of the school and go to a different one that guarantees a pass.
If you looked at the ONET list of students that school put out the one thing they donot mention is that 90% of the students take extra classes