I'm really sorry to hear about your experience Jai and it's bound to have shaken you. It's hard for any of us to work out if a school is going to be a good fit at the best of times.
Private schools can be tricky, well any school really, because they can make promises that aren't fulfilled. Is it possible for your son to have a couple of trial days at the school? That way you will get a sense of whether it might work.
What we look for in a private school is the same for any school, a productive flexible environment where our child feels comfortable. There is the difficulty that much of that is teacher dependent so you can have good years and bad depending on the teacher. Do you think that might have been a contributing factor to what is happening at the current school. Difficult children and a teacher who struggles?
Regardless, it is important to visit prospective schools and try and get a feel for the atmosphere. Is it rowdy or calm, happy or rough, does there seem to be respect between the children and the teacher, do they value the parents? Remember it will be your experience that is important too. Can you communicate with the school? Even if they don't know have all the answers are they willing to work on it? Do you know anyone who has had a child there? Personal recommendations are useful but of course, every child has different needs so take them knowing your child could be different.
There are resources around, try the Hoagies site for what to look for in a school. Good luck
