Was it the Asian food delivery van?
It's a hard one. You have to find a way to discourage people who live 5 mins walk from the school not to take their cars. I know one mum who lives at the bottom of montpelier park and drives to school.
The school ran a campaign about double parking last year and got the kids to design posters. The community police officer based at boroughmuir got involved and for a while they had police traffic wardens at pick up and drop off times. I've been caught up in the traffic agro there a few times when I've picked up or dropped off with my van and now I won't go near the place with the van unless I'm really running late back from work at the end of the day. Normally I'll park the van at home grab the bike and scoot up the road.
It's hard to not sound preachy to these car obsessed school runners and as you see them every day and some of them are your friends don't want to get into a "political" argument. I try the jokey approach with them... I'd love to see a the school do a sponsored cycle to school week or something along those lines. Maybe Mr SRD and I could try and slip that in while we do the cycle training.
The best thing is to lead by example and get the kids to cycle to school. I see more and more bikes at the school every year that goes by.