If you’re talking about the Gun Free School Zones Act of 1990, the Supreme Court did indeed rule it unconstitutional as an overreach of the interstate commerce clause. However, it was quickly amended to be limited to firearms involved in interstate commerce. The SC has not ruled on the amended law, but several lower courts have upheld it, so it is current law. There is also a Gun Free Schools Act of 1994, which stipulates that states receiving federal aid for schools are required to suspend students found on school grounds with firearms for no less than one year. The constitutionality of that law has not been challenged.