A spokesperson at University of Alabama Hospital at Birmingham said Miller was in the trauma intensive care unit.
The accident, which involved no other vehicles, occurred on Jones Road in Dearmanville, the community in which Miller lives.
Oxford City Schools spokesman Roy Bennett released a statement from the Miller family: “First, we would like to say thank you to our heavenly Father who is in control. We want to thank everyone for their cards and visits. We would like for everyone to continue to pray for CJ’s recovery.”
Miller teaches 7th-grade science, according to the school’s website.
This story will be updated as more information becomes available.