My understanding is that the federal law is never enforced except as an added charge to other offenses.
Your "understanding" is dangerous. I have a good friend, war hero, convicted by Feds because they "surmised" he had knowledge of something someone else had done. Long story. Take nothing for granted re: the Feds.
The school zone laws are a genuine infringement, IMHO. In many/most rural areas every pick up truck waiting in line to pick up a child after school has a gun inside. This is a major issue for me as I am a reenactor and used to speak in schools carrying a Rev. period flintlock rifle. That is now illegal and I cannot do it anymore.