Why does traffic get so much worse come fall?

I go into work around 8AM and traffic is remarkably worse come September 1st. It's infuriating. I normally hear this attributed to school being back in session, but I don't get it. Is it the fact that now all teachers are on the road that causes increased congestion? But they go into school much earlier than I go into work, and I don't think teachers are uniformly a poor set of drivers, nor are there so many teachers that the sudden advent of their being on the road would cause such a dramatic increase in traffic. Is it the parents of kids that change their schedules due to having to take their kids into school? But they'd be on the road anyway going to work, right? What gives here? Why the precipitous increase in congestion, delays, etc. once school starts? What is the mechanism behind it? AND HOW CAN I STOP IT?????