First day on the job as a kindergarten teacher, he asked a little boy what 5 and 5 added to. The boy froze. The young teacher rephrased it more concretely to help the lad. "If I give you five white rabbits and then give you five more black rabbits, how many rabbits will you have?" The boy paused for a moment and answered, "Eleven". "How can you come up with an answer like that?" "I have one at home".
This was related by Paul O'Brien at a folk music evening in Sidney B.C. (Deep Cove Folk) and he heard it from his daughter who had just graduated as a teacher from Queens University and she heard it from the professor who says it was his own story.