@TizerorFizz sorry, of course he knew he was kept back! But what I meant was, they would not understand the reasons why. They just accept what you tell them. In my ds case it was because he entered the school through the French way, which meant he had to start MS/Reception age 3, turning 4 end of October, just like his little sister is now doing (her bday is December). The only difference is, she is doing fully French, so we will just switch her to the British side, which is bilingual when she is the correct age for Reception. For my son, at the time this was not an option, so he had to start in the MS/Reception bilingual stream at age 3. But when he got a spot via the British side, he had to repeat the year because he needed to follow the British entry rules. Very complicated. But anyway, in the end it suited him much better. We told him the reasons why and he accepted and did not question it. He had no problem with making new friends. He was so young, he forgot his old friends and just made new ones. If he was August born and we made the decision based only on he was not ready, then I would just explain it in the same way. You are summer born, so the youngest in the year, you have the option to repeat so you can be the eldest in the year, which is better for you. You will make new friends. Let's celebrate this new decision made with a dinner out and a special gift....or something along those lines to let the dc know it is a good, fun and special thing....not something that is unusual. If you make it seem fine and something good, the child will believe it and move on from it, but if you dwell and give off the wrong vibes, I think the child will feel this.
My only other experience of this is my childhood friend, who simply told everyone she had to repeat because she was too short and she went on to have a very happy school experience, no problem. People did not question her further and tbh I am still not sure why she even repeated the year! I assume because she was struggling at school. But no one ever asked her again except for the first time when we noticed she was repeating and that was it. And both of these experiences were fine. AND also even my dd says they constantly repeat stuff in her year (year 6) and she is super bored and she never repeated....so I think they repeat things sometimes anyway to help the children retain the information.
But like a pp said, if there are other issues at play here repeating the year will not simply solve the problem....it really depends what it is. When a child starts too young, it does impact them. My son was only two months away from an August birthday and when he started a year early, he would be falling asleep sometimes at the end of the day, had a few wetting accidents, could not read past stage 1 by the end of the year....he just was not ready and I did not push it. After he repeated the year and was in the correct year, he never had another accident at school, never fell asleep at the end of the school day again and he quickly went from struggling to reading to way ahead and now top of his class, exceeding in math and English. I believe my ds is a bright child and would have eventually caught up if we kept him in the year he was, but so glad we did not push him through. There is no rush to finish school.