It is a hard balance and I liked your analogy about not artificially moving shelves higher for taller kids. However, when I thought about it, I found myself thinking that, while we don't move things to places where tall children need to reach, we also don't force them to use a step stool in the bathroom to reach the sink if they don't need it nor do we place the shelves so low that they need to bend down to reach them.
I totally agree with you about not focusing on the grades. That's been a challenge for me b/c one of my girls is grade accelerated which has her being compared to grade mates who are, on average, 18 months older than she is (late bd coupled with the skip). I know that she'd be a straight A+ student by simply showing up if she was in 8th or 9th grade this year rather than 10th, but our main purpose of "pushing" her so to speak was so she would learn how to work.
I find work ethic to be something vital that I want my kids to develop. I will temper this by saying that we didn't really "push" dd or her school into skipping her. The school approached us and dd was on board. My other child is more of an academic slacker so it has been harder when it isn't as self led by the student.
I'd say that it is fine if he isn't reaching his full potential as long as he is engaged and learning something, whether that be another language, or something else. When it gets to the point where the child is developing poor work ethic b/c the only requirement is that s/he grace the teacher with his/her presence on test days to get As, then perhaps a little pushing for more challenge is necessary. Neither of my kids is being fully challenged in all subjects. My oldest will probably never be challenged in her strongest subject and pretty much never has, but there are some areas where she has to work and that seems to be enough to learn how to work.
