I think you should walk to school if you can. Say if the school that you're going to is less than a 15 minute bike ride, peddle to school for exercise, and then you would stop the busing for school, which will stop gas prices from going higher because of all the cars in the world that need gas to move.
Because if you are late for school, so you can't walk to school, you HAVE to go by transport, either you will be marked late for school and it will affect your grade. And you will be considered as irresponsible student for your life time which will be very bad for your future.....
Of course you should take transport. The amount school bags weigh is a lot, generally a few kilograms which is a lot for a young kid. Walking to school will make him tired before he can even reach there and will distracted. Also look at the fact on what happens if it rains, all the books get wet, its a waste of resource, this will not occur if someone uses transport. Even car-pooling comes under transport and its an awesome idea. Kids shouldn't waste their time walking and should go in school to using transport as is more effective.
Its faster than walking, and here in Toronto its $3 for one way on the bus, and for a student its $2 so its not that expensive for a person living in an expensive city but get used to it walking means you have to set your alarm earlier to wake up on time, and I bet you, your parents won't let you walk .. The only con though is traffic.