My daughter is studying in N1 (am class) now and she enjoys it very much.
Last August, she was just two years old and it took her one month to quit using "ampers" with the help of teacher and the influence of her peer group. There is no difficulty for them. So don't worry and don't force your son to quit "ampers" before the school starts. Let him do it naturally.
The teacher and amah will teach them how to go toilet and wash hands.
They also tell the children how to fold handkerchief and distribute the refreshment for them during tea time.