Holding kids back works in athletics and academics.
Private schools have perfected holding kids back or doing a prefirst. There is no longer any stigma for doing this. Years ago anyone held back was looked on as lacking in something.
And along with hardly anything considered wrong now a days except being a white male. Holding back in public isnt looked down on either.
So you have no reason not to hold your child back?? There is no question that there is an advantage.