Classes are far more likely to cater to the weaker kids. And if a kid is having problems there is nothing to say that their parent can't help them. Why care how a grade schooler scores in a standardized test? And there will always be someone better at sports. I could care less what other families choose. It just isn't my problem. And, no, mine weren't.
It isn't the parents problem...but definitely can be the younger child's problem, unfortunately. One of the first things I told my 4 year old Kindergartener's teacher is that if I saw ONE indication coming home on her report card (difficulty sitting still....following instructions....etc.) that she was compared to SIX year olds in her classroom to receive it - I would NOT be happy. Average 4 year olds do have a bit more issue sitting still...following instructions, etc. than 6 year olds. That's normal and expected and since that classroom was made for 4 and 5 year olds - do not hold my child to standards set by a child who should be in 1st grade. Luckily, my dd's K teacher also had a 4 year old child starting school that year - so she knew exactly where I was coming from. DD has done fine, but it COULD be an issue if the teacher was not realizing the differences in maturity that should be there due to age differences. Unfortunately, as much as they try to avoid it - kids are compared to each other (higher reading group....lowest reading group, G/T, etc.) and I don't want my child being compared to a child 18 months older than she is. She can hold her own very well with her peers but I (nor anyone else) should expect her to hold her own with kids that much older than she is. So it does affect us as much as I wish it didn't. It affects every child who should be in that class, not just the young ones.