The overarching message is that, no matter how old you get, you still have moments of insecurity and unsurity that remind you of times when you were a child. At times, you still feel 11 inside.
And the story within tells of this terrible incident in school where the teacher embarrasses her and makes her regret not being able to speak up for herself. You can derive a lot from that, but I think it mostly focuses on how kids are often too intimidated by authority to speak out and defend themselves.