I don't screw it on really tight
I think this is key. I make it tight enough so it doesn't leak, but no tighter.
At our school, the teachers are not with the kids in the cafeteria because that's their break/lunch time. There are cafeteria helpers, but it's loud and it can take the helpers a long time to notice that a kid needs help. Whenever I visit my kid at lunch time, I'm always helping kids at the table open food containers, juice boxes, etc.
Beth, mom to older DD (8/01) and younger DD (10/06) and always missing Leah (4/22 - 5/1/05)