What divorce laws would make the child change their last name?

My boyfriend's last name is "Ramirez". His parents are divorced and he lives with his mom. He went to a school that one of my friends went to in 1st and 2nd grade before his parents got divorced. My friend brought their 1st and 2nd grade year book to school so I could see my boyfriend when he was little. His last name was "Lopez" when my boyfriend was in 1st and 2nd grade. Would they really make him change his last name over his parent's divorce? and my boyfriend sees his dad regularly.