As a preschool special educator, I have to agree with you that things can't continue as they are -- it's not fair to him, and it's not fair to you. At the same time, it's been a really short time, and I'd probably try some other things before I just gave up.
1) Can you stay and "narrate" his day for him a few times? Having someone stay and talk through the day (look, it's circle time. All the friends are going to circle, it's fun, come sit on mommy's lap at circle.) can help kids get the message that something is OK.
2) I agree with leaving for short periods of time and then gradually building it up, but wanted to add one caveat. In my experience, when parents prolong drop off, the kid is anxious the whole time they are waiting for the parent to leave, and then they associate school with feeling anxious. Given that, I suggest that parents follow the same quick goodbye ritual they plan to use all year, drop off leave and then come back and stay. So day one, drop off, walk to the water fountain have a drink, come back and say "See, Mommy's back and I'm not leaving today", and then play with him at school, and take him with you if you have to leave again (e.g. to go to the bathroom). Day 2, maybe you stay out of the room for 5 whole minutes.
3) Do they nap in the afternoon? That can be really hard for kids at first, maybe you could have him go home before nap each day, and just do a 1/2 day.
4) Would the teachers do a home visit? Having your teachers in your home, being treated like treasured guests, is HUGE for a lot of little kids in building attachment and trust. Would they be willing to come to dinner with you -- sharing a meal is really powerful.
5) Maybe make 2 photo albums, one of school, and one of home. Leave the school one at home and look through it and talk about his day, and vice versa -- leave the home one at school as a transition object.
6) Have someone else drop off -- leaving your primary attachment person is harder than leaving anyone else. I know my son cried at daycare if I left, but if my mom drove him he was fine. Could dad take him for a little while?
If none of those work, then maybe he's not ready, or maybe integrated is too much stress, and he needs a smaller classroom, but I think there are things you can try before you just pulled him out.
Good luck!