A few years ago I was doing contract work. I rode a lot more and at all times of the day. There were many many routes that were very nice.... Except during rush hour, then they ranged from not so nice to outright dangerous.
I think that does a lot to work against biking to school. Where I went to Grade school a standard back route for commuting goes past 2 sides of the school. That means 3/4 of the potential bike riders have to deal with that nastiness. It may be that it is not too bad right at the school, but I know it is only a couple of blocks away.
For me biking was out of the question. I was too close. With the bike rack on the far side of the school from me it meant almost doubling my distance.