R.,
I am a preschool pastor and have seen many, many children go through the same thing. The best advice is to just keep doing what you are doing. You obviously have been advised well by others about things like giving him to the teacher and getting away quickly. Just be sure you don't sneak away from him; always kiss him goodbye and tell him you love him and will be back soon. But there are a couple of things that we have tried that may be helpful.
You talk like it is usually you who is dropping your child off at the door of your child's room. Whenever possible, try letting your husband take him to class instead while you head in a different direction. Sometimes this works, sometimes not, but try it.
Also, usually children prefer to walk into their classrooms on their own instead of being carried and handed over to the teacher. Of course, if he is throwing a fit, this may not work, but try letting him walk into the building and down the hall with you holding his hand. Then when you reach his room, open the door and let him walk in. Hopefully, his teacher will meet him at the door, stoop down to his level to welcome him and immediately direct him to something in the room that will catch his attention. She might even have something in her hand that he would like to play with that she can share with him right away to get his attention off you.
Be sure to talk with your child about fun times at church when you are at home with him, and not just when you are getting ready to go to church. Find out some of the activities his teachers do with him at church, and repeat those activities at home, while at the same time you remind him that he liked doing this at church, too. If he has a favorite toy in his room at church, and he possibly has the same toy at home, remind him that he likes to play with that toy at church. Just work going to church into your conversation with him multiple times during the week, always in a positive way.
But the best advice is to keep taking him to church and other places on a regular basis. We see a big difference between children who only come to church sporadically and those who come weekly or more. But even regular attenders have difficulty sometimes, and these are children who don't like change. It just takes them longer to adjust. My hope is that he has the same Sunday School teachers each week so that he greets a familiar face each time.
You are doing a good job, Mom; just keep doing it and one day he will surprise you and walk right into class with a smile on his face.
You may email me if you would like at ____@____.com Hickman
Associate Preschool Pastor
Lake Arlington Baptist Church
Arlington, Texas