What do you mean by "technically"?
No state code "supersedes" Federal law.
Let me rephrase that so everyone understands. Under federal law, schools are a gun free zone just like post offices and government property. The exception to that (in Missouri) is that if you do have a Missouri CCW permit, then you can legally have a firearm on school grounds as long as it stays in the vehicle and you do not brandish it.
I did link to the corresponding Missouri State Statutes