N.D.
My little one has been in daycare for 1 yr now, and in Sept she transitioned to Preschool full time from being part time. In the beginning, I remember it was very hard for us and her. She'd do exactly the same thing -- throw a huge drama when we dropped her off. But 5 min later after we leave, she's fine and the whole day she's fine. It's normal and the teachers will say so too. It's more harder on the parent than the child.
I agree with what the others say. Drop off, give a big kiss and goodbye hug, and l-e-a-v-e. Just go. Don't show that you are sad or it will just make it worse. Show that you are happy and excited and confident and that will exude on him.
Even now my daughter still gets a little sad when I drop her. But I firmly say goodbye and just leave. Always later I get a report from the teacher that she did just fine throughout the day.
Also I agree that it helps to get the child excited about school. The night and morning of school, I always get her excited by talking about the things she will do there and I make myself look all excited and thrilled about it.
Good luck and this soon shall pass. It's very common for them to do this. Don't feel sad, he's going to benefit so much from being in preschool! My daughter was speech delayed and in just a mere few weeks of preschool her speech and socialization skills have skyrocketed!
It shall soon pass. Just do