Yeah, you don't know it till afterwards, as with most things.

DD refused to put any weight on her feet till she was 13 months old, which was why we went to the physio. Still no idea why. I try to discourage the W sitting, but she can't sit another way without a chair. And same sleeping posture, too! It's cute, though.

It hadn't occurred to me that she might have trouble at school, but of course she's going to find it hard to sit on the mat and at a desk, amongst other things.