Sign in? Ha, that’s a joke. Schools can have three dozen outside doors.
They're all locked so you can't get in and usually have signals that go off if someone opens them from the inside. Many schools even have metal detectors. This is a large high school. I can't imagine that these security precautions weren't in place.
Back when I substituted (until five years ago), I was very cognizant of security precautions, having to adjust to different systems every day. What I've described is the minimum, precautions all schools have or should have in place, especially after Sandy Hook demonstrated it can happen anywhere.
Yes every school in CA has dozens of outside doors and kids eat outside too daily. Warm temps and little rain.
Every classroom opens to the outside and there are lots of portables too in CA.