This is not normal, Emma. It did not happen when I was young...and to accept it as normal is highly dangerous. Children did NOT carry weapons to school in my day. I am 55 years old this April, I lived through those school years, went to the worst one in my area, and it was not a place of violence.

I think this is more down to perception of knives as weapons. When I was in high school (65-73) I carried a knife most days, but it wasn't deemed to be a weapon, it was a tool to be used in various situations. I would never have considered using it as a weapon.
The fact that Lizzie never saw the knives does not mean they weren't being carried.