It will probably take 2-3 weeks for him to get used to the new school. Here are 2 things that helped my 2yo when she started a new school:
1) ask the teacher to meet you at the door of the classroom. Take a minute to talk to the teacher while you hold your son so she can ask him what he wants to play with today. Say goodbye to him, let him know you'll be back later, and then let the teacher take your son into the room. It sounds weird, but it really helped my daughter-- since I talked to the teacher for a minute, my daughter could see that this was a nice place to be (I was not anxious about being there), and since the teacher took her into the room, SHE was leaving ME to go explore, rather than ME leaving HER.
2) This is another weird one-- Have a friendly, upbeat conversation about how he can choose his feelings. Discuss it as if you were letting choose his dinner-- no negative emotion attached to it. When you drive into the parking lot, ask your son if he has fun playing with the toys at school. Then ask if he would rather be sad at school, or choose to be happy at school. Remind him that he has fun at school, so let him know he can be happy about being there. Tell him that he doesn't have to cry-- he can CHOOSE to be happy to be at school. I was dumbstruck when my 2yo didn't cry for the next 2 days after our little conversation. (the second day, I asked her if she wanted to cry today or if she wanted to choose to be happy, and she said she wanted to be happy). Now, as a disclaimer, after those 2 days was the weekend, and she cried again on Monday. But that week was the last week she cried when I dropped her off. Kids love choices, and even letting them know it's ok NOT to cry can be very empowering for them.
So just hang in there-- he really WILL get used to being there. Good luck!!