We transferred DS from one school to another last year for 1st grade. We told him as soon as we decided and he was part of the process - went on school tours with us, took a standardized test with the new school for admissions, met the classroom teacher etc. We told him that the new school was more rigorous academically and that he would be less bored there. He has transitioned well and was happy about the move. So, yes, do let him know early (unless you don't want the current school to find out about your move) and keep talking to him over the summer about the new opportunities the new school brings. Also take him to the new school for a tour and to meet the teacher and other students closer to Fall, if possible. And my son's new school gave us a bunch of curriculum they use for K and told us to review them at home if possible so that the child has an idea about what went on in K. Which turned out to be a great idea and helped the transition become smoother.
