I went to primary school in the 80s and 90s and even back then it was pretty hard to be held back a grade level. Typically it only happened when a kid missed a lot of school, like they were hit by a car and spent 2 months in the hospital. Failing grades alone didn't usually cause it, at least the kids who seemed completely uninterested in school still somehow managed to graduate.
"Everybody is a unique snowflake" attitude is causing way more problems then we publically admit. Setting boundaries is important. As is seeing the consequences of your own actions. I was held back in school for a year. Looking back, this was one of the most important things in my school time. I am glad it happened.
