crying at school

my kindergartener recently started crying at all times of the day saying that he does not want to go to school. After several days of prying, he finally confessed that a kid at lunch is picking on him. My husband told the teacher but he still is crying and refusing to go to school. He just turned 5 and had been with grandma until now. I have tried talking to him until I am blue in the face reassuring him that he is not alone and that we have to work and he has to go to school, and although he seems to be listening, as soon as I finish he goes right back to saying, he does want to go to school. Are there other tools out there that might be able to help me and my husband?