DS (3, almost 4) goes to partial-day pre-school, and rides the regular bus home at the end of the day. Lately, he has been getting into a lot of trouble on the bus, getting up out of his seat, climbing over the seats, running around, etc. The bus driver warned him (then came by the house to talk to DF, to let us know what was going on) that if he didn't behave, he would have to kick DS off the bus, at first, for one day, at second incident, for the rest of the year. DF talked to DS, I talked to DS, and my mom talked to DS this morning before he got on the bus. He said he understood, and that he would behave. Well, he didn't. And now, he's kicked off the bus for tomorrow. I don't know what to do. I've tried telling him that if I have to quit my job so I can go pick him up, that that will take away money for us to do extra fun stuff (I'm going to be putting my notice in in the next 4-6 weeks, anyway, so it wouldn't be just for this), and he said he understood, and that he would behave, but he didn't. I've tried talking to him about safety, and how he needs to stay in his seat so he doesn't get hurt, but that didn't help, either.
Any ideas on how to get him to behave, and stay in his seat?