Because of federal law related to school funding. Off the top of my head I cant remember the law, but in summary barring a court order to the contrary each school is obligated to give both parents access to all school records.
If your court order does not specifically state you are entitled to those records then the school does not have to give you access to those records.
Over the past few years reading the school handbooks my kids come home with the wording has changed. This year I was suprised to read something to the effect that children of divorced parents are entitled to have lunch, have each parent volunteer in the class room, and various other entries regarding children of divorce.
One section seems to be in the "warning" tone that baring a court order restricting access both parents are entitled to all information sent out by the school, and the school will send information to each parents address with out notice.
As for legal custody, if the issue is unresolved what happens when a decision involving legal custody has to be made? (I know... probably chaos...).
In our bass ackward county that has jurisdiction??? Mom gets final say. In the words of the judge mom is around the kids for the majority of the time and dad needs to understand this. Dad needs to understand that he does not deal with day to day issues and mom knows best.