>to keep kids, parents & teacher in and the rest of the public out.
Facial recognition doesn't do /any/ of that.
Teachers have always been able to tell when students are skipping school, that's what roll calls are for. They work just fine, wayward students just don't care and skip school anyway. If you want to ensure your kids stay at school, maybe we should take the money spent on facial recognition systems and spend it on training our current teachers and paying teachers enough that the best in our society start seeing teaching as a viable career.
As for keeping the public out, we've had a purpose-built tool for this for millennia, it's called a gate. CCTV at the gates is every bit as effective as facial recognition in the halls. If people are going to ignore the implied warning of a gate with optional CCTV, adding facial recognition in the halls won't help. Such people will just lie about being a tradesman or public servant or whatever. Either they'll be convincing or they won't. Most of us would recognize a stranger in our office, the same is true for teachers and other staff in schools. They already know this person is a stranger, they don't need a facial recognition system to tell them that. If you're worried about incursions from the public, the money would be better spent on training teachers for that situation or if you must, hiring good old fashioned security guards.