The original GFSZ Act was ruled invalid and unconstitutional. The Federal Congress almost immediately rephrased and passed another GFSZ Act that has, so far, withstood all challenges.
Under the Federal law, if you have a licensed firearm (licensed by the State in which the School is located), you are clear of any wrongdoing if you are found within the 1000 ft. area. You are not permitted to actually go onto the campus (but your State law may be different - this is allowed under the federal law).
So... If you are walking/driving/passing through that 1000 ft. radius and have a State permit, you are OK. Note well, that your permit must be issued by the State in which the School is located.
This is only the federal law. Your State law may be (and in most cases, it is) different.