Sadly, it's exactly the strip I thought it might be.
Panel 1: As he and Lawrence put on their coats, Mike yells "I missed recess and I had to write lines and I'm never coming back to school! NEVER!!"
Panel 2: He then yells "I got kicked out of the library and I hate my teacher and it's all HER fault!!" Lawrence asks why.
Panel 3: Mike turns into what looks like a horrifying genetic mash-up of Linus Van Pelt and B.D. from Doonesbury as he growls that she caught him mashing spitballs in the dictionary.
Summary: Ordinarily, I wouldn't pay the blindest bit of attention to a tantrum like this; the idea that the teacher is a bad person for punishing Mike for misbehavior instead of letting him get away with it because the world is supposed to revolve around him is, sadly, something a six-year old would think. The problem I have is that the Mike that was about to deliver a long, boring and probably insulting speech at Liz's wedding never grew out of thinking like this. Like Elly before him, he thinks that everything is someone else's fault.