Reluctant to attend the school

Hi everyone,
My kid is 3yr.&4months old. He started going to preschool from this september. But, last yr. je used to goto the same class and same teachers. Now, suddently he became so reluctant tht he doesn't want to go anymore in tht class ALONE. He wants me to stand there and he doesn't want to speak to the teacher. Now, from today he doesn't want to go with me. He goes to other class where parent are allowed and he's very happy there.
I need your suggestions or advices, if any of u guys came across with situation similar to this.
Thanks,
Richa