Our kids are 7, 9, and 11, and all are good bike riders. We go most weekends to local parks and such with the bikes. But we have not had them ride bikes to school.
Our school is not far (less than 1.5 miles), but there are two very very busy roads between our home and their school, and our city is not very bike-friendly for adults, much less kids. Almost every driver here has a cell phone in hand with the car in motion.
We have ridden to their school together on a weekend now and then, on early Sundays with very little traffic. DH wants us to ride with them on a Friday (more relaxed school and work day) to get them used to it. Our 7 year old is fearless, but that gives me more agita b/c he thinks he can dodge any obstacle, and he can't. Our 9 year old is a bit of a nervous rider, only comfortable with zero obstacles, who freezes in the face of any possible danger. Our 11 year old is more balanced, but he's less interested in biking to school and will need lots of encouragement.