OP here. The teachers say he is pretty happy the rest of the day. They do the usual activities - playground, art, circle time, lunch, nap, etc.
I have tried of variety of things at dropoff - staying longer until he is settled, making a run for it, etc.
Also, I should have mentioned, this battle starts first thing in the morning. He wakes up and immediately asks whether or not it is a school day. If it is, he has a massive meltdown. We have breakfast, get dressed, play and he is fairly calm. But as soon as we make for the car, it's a litany of I don't want to go for the next 15 minutes until we get there.