What should a person do if a school, daycare or doctor is ignoring their legal standing as a parent. The first part of the question is that I want to explore whether or not you really do have legal standing. You may know you are the birth parent of the child but that does not necessarily mean that you have legal standing. You need to look at the rules in your state.
In some states it is enough, if you are the father for example, the fact that you are listed on the birth certificate can convey legal standing. It shows that you are the legal parent of the child. In other states, the fact that you are on the birth certificate may not be enough.
Part two of what you have to look at is whether or not you have a court order for custody and parenting time. Because for some schools, daycares and doctor offices the fact that you have a birth certificate which conveys legal standing or even the fact that you have a court order which says that you are the parent or that you are ordered to pay child support, that may not be enough.
You may also need an order by the court saying that you are entitled to certain custody rights. In other words, that you have joint legal custody with the other parent or that you have sole legal custody of the child or children. In addition, it is very important for your parenting plan to be very specific about the parenting time that you are awarded of your child and children.
I've had some cases where a school wouldn't let a father go and see his son during the lunch hour because the parenting plan didn't say that he could. So the school was limiting my client's time to only his days.
If you don't want a mixup like that then I would encourage you to either ask the judge during your hearing for specific orders about things like that.
But when you have legal standing combined with a court order for custody and parenting time you should be good. I haven't seen a situation where a school or daycare or doctor's office ignores a court order.
Another thing I want to add to that answer is there are situations where the other parent gets in the way of the other parent despite a court order. They make it difficult and if this is happening in your case then I would encourage you to take a look at finding some sort of request to enforce the court order with the court.