If you have sole legal and physical custody of a child then yoou have all the parental rights and control of the child.
For example,
medical/school decisions, access to records religious decisions right to leave the state or country without needing the other parents approval.
Step2
If you have joint legal custody with visitation. Then you both have access and have to make joint decions on everything I listed above. If you don't you can be found in contempt of court and you may have to go back to court to have the court make the decision.
Step3
Anyone with joint legal has a right to get access to their child's medical and school records. Some places are strict and you have to request the records yourself if you are not the primary caetaker, but you have a right with a copy of a court order. If you have a court order for visitation and it is denied you can go to the police to help them enforce it or go back to court. You might have some problems if you live in another state. Some police may not enforce a court order from another state.
Tips & Warnings
Check with a lawyer in your state to know your rights. Most Probate Courts have a lawyer of the day program who can give you free legal advice.