Legal Question : Precedent and how many times does one have to get a ruling on the same issue...

One of my pet interests is appropriate separation of church and state... particularly regarding public schools.

I regularly read stories of teachers, coaches, and school administrators preaching the 'good word' on school time to a captive audience.

Often, an organization like the Freedom From Religion Foundation will take up the case and write a letter and if the activity isn't stopped then a court case can go forward.

At what point is something, not even this specific issue, considered to have a legal foundation and bringing someone in a X vs Y court case in unnecessary?

IOW, at what point can someone make a call to the authorities and report that a law is being broken and it is on the government to investigate and prosecute as opposed to a private organization bringing the school etc.. to court?

"I've been robbed" " My civil rights were violated" etc.. etc..

Or is it always necessary?

I believe that I understand that the issues can be re-adjudicated at state levels based on state laws but what about a federal mandate such as the establishment clause?

Clear as mud I hope... I feel like this is a basic concept but I must have missed that specific day of civics...