When I was in school it was effortless to attain pot, and for that matter LSD, cocaine, and with a bit of asking around just about any substance you cared to partake of - with the exception of 2, alcohol, and to a lesser extent tobacco. These actually took a bit of effort to attain, and especially for alcohol it more often than not came up empty handed. All good, pot was always a phone call away on the weekend, or if it was a weekday I could just pick it up at school. That has not changed one bit. As long as unscrupulous individuals control the distribution there is absolutely ZERO control over whether or not our children can get their hands on it.
Legalizing pot would make it MUCH more difficult for a child to attain.