I guess I have a different view, and think it depends on the kid. My kids both seem to have a fantastic grasp of grammar, mostly picked up informally. It is possible I am minimizing what they have learned in school- they are taught grammar after all, but they are years ahead of what is being taught and still seem to know their stuff. They never make errors or need editing. They are the same with spelling, which I also feel was totally unneccessary for them to learn in school. I assume they picked it up from their reading, conversation, etc.
I do think every kid is different, but I would have been happy if mine were allowed to use grammar and spelling time for other pursuits.
ETA: on re-reading this, perhaps my frustration in this area is related to how low the bar is set in our school in these areas. If there were appropriate instruction available I might have a different opinion, I guess. Still, it doesn't seem to be an area in which we felt a need to supplement.
I think that I made very few grammatical errors as a kid, but I still feel like direct grammar instruction would have been hugely beneficial. I agree that the bar must have been set pretty low even in the advanced LA classes at my school.
