Exactly the same situation as my son last year in PN.
He was talkative at home and did not even speak or move in school after a couple of weeks. He cried so badly every morning when he needed to go into the school (stopped after going in). It went on for 2 months.
We found that the teaching method and many other things made him feel uneasy in school. We transferred to another school this year and he did much better (he even says he wants to go to school on Saturdays and Sundays).