Dianne how scary and I'd be pretty cranky at not having been notified. I guess though it may have been a pretty low level event (I guess a kid taking a knife to school without specific malicious intent is very different to someone coming armed with a purpose in mind), one of the teachers may have triggered the lock down as a precaution rather than because there was any degree of risk, kwim? Still, as a parent I would still want to know, so it's worth speaking or writing to the school about it.

we went into lockdown and the 'safety' measure they had for us was to lock the classroom doors and hide under the desks lol.
That's pretty much what a lockdown is, still, except they train the kids up to get to the nearest safe lockable area (if they're outside the classroom), lights go off and curtains drawn, and they have different sirens depending on the nature of the emergency. At our last school there were two tiers of emergency, one was called a lock in and one was called a lock out (couldn't tell you the difference) but they practiced it regularly and the kids all knew what to do. Cass what a horrible thing to be caught up in and clearly demonstrates why schools need to have good lockdown practices.