I’m currently attending ISB 
ISB has around 250 people per year, and as one of the top Thai International schools, we have around 70% international students and Thai students are capped at 30%. Most of the international students come from America, and also some from japan and korea.
ISB is a IB school, but we’re very american in that we have GPA’s. School doesn’t rank. Theres a lot of variety in what curriculum and how rigorous they go. You have options of taking Full IB, Partial IB, or just getting a regular ISB certificate. The top students usually take 4 Higher Levels though and these are the students who get into ivy leagues etc.
Teachers care a lot about how hard you work and how well rounded you are, and we have a class president, vice president, and class representative leadership positions which are based 100% on student voting. So you really have to be liable to stand out and to be elected, you need to give a speech and win the popular vote.
I think in general ISB teachers are really nice, but quite bad at teaching. They are helpful outside class, but at the same time, I feel like teachers put more importance on being friendly than being a good teacher. A lot of students go to private academy to supplement teaching.
Extra-curricular wise - ISB is great and it’s very easy to start a club as long as you have good intentions and teachers are always very supportive. The top varsity sport teams are most respected in terms of extra-curricular.
One of the downsides recently was a house system they started last year. School is divided into 4 Houses but noone likes the system and it doesn’t work well with ISB culture. I think that might be erased soon.
We have 5 counsellors who meet us in senior year. You can meet them when you want and they can be somewhat useful.
Overall, I think ISB is on par with BPS as the top tier 1 schools in Bangkok.