they felt he lacked maturity.
Lacked the maturity to sit still for a full day of 'easy-peasy' work, where he learns very little, like his big sister? ((Just guessing here!))
In that case they are doing you a favor!
Flexibility is what you need from a school. Same old same old at a slightly earlier age isn't the same as actually being willing to analyse what the child's learnig level is and bringing him to the classroom that is a match.
Especially if your son doesn't seem immature at home, I think that they are pulling your leg.
Grinity
