So how would you build or design a school that controls access without making it impenetrable for LEO or difficult for children to escape?
My bank has a normally locked front door. I have to be buzzed in.
As for glass, we use tough glass to build new houses here in Florida.
Steel doors are common.
Do not build the entry points in such a manner as to prevent a “break-in”. On example of a bad design was to create a wall composed of windows too narrow for the average adult to get through .... 9” wide if memory serves. The design was for a span of brick wall, a 9 in window another span of brick, repeated up to the entrance door.
It would be better to have break resistant glass (but still breakable). This would allow emergency personnel a means of still getting in a whole lot faster than the above.