Where do they learn this stuff?

Elijah has had some problems at school lately. He thrives on routine and any disruption in routine causes a disruption in his behavior. Well, our lives have been nothing but disruption this month. He missed school for two week when we went to Canada, then we had the stomach flu, then he got the stomach flu, and Eric was gone to FLAME classes in Michigan for a week, so Miss Pam has remarked at his change in behavior and we've been doing our best to give him consequences here at home for his school stuff. Anyway, last week he brought home a review paper on opposites. He had to draw lines between the opposite objects (hot & cold, big & small etc.) and all of the lines were drawn correctly. I was holding him on my lap praising him for doing such good work, trying to encourage his good behavior to help curb the negative yada, yada, and he looked up at me and said, "Mommy, I didn't do that." Huh? Who did? "Ellie was sitting beside me and she did it for me because I didn't want to." Great, and he's only 3 years old. Is this a sign of things to come? I wish I had pictures to post, but the camera is still broken. Maybe we'll get each other a new one for Christmas. Anyone have any suggestions on a good digital or what to do with a 3 year old cheater? :)