Do I become custodial parent if the custodial is incarcerated for a felony and cannot bond out?

My son's mother has been incarcerated for 5 counts of fraud identity theft. She is the custodial parent and I am the noncustodial. I live in Austin and they live 60 miles away. My son is staying with her father but I am wanting to bring him to live with me. Am I allowed to withdraw him from his current school and enroll him in a school where I live while she is in jail? What steps do I need to take to do this the right way?