The Children, Schools and Families Secretary confided to a group of Year 7 pupils last week that he was not the best-behaved child.
"We had detentions where we had to stay behind after school for an hour," he said. "I got seven or eight of those. I used to go on to the roof to get a ball down - silly things like that."
Of course, it did not seem to do him much harm. Mr Balls went on to Oxford and then Harvard, before becoming the Prime Minister's closest ally - all this despite telling the Year 7s that he "was never the brightest child in the class".
Equally surprisingly, Mr Balls said that when it rained at his school, the water came gushing in through the roof. This seems unlikely if he was referring to the well-furbished, private Nottingham High School he attended. But it could explain his eager support for Building Schools for the Future.
Meanwhile, there was a revealing verbal slip from Mr Balls' colleague Jim Knight, a schools minister. Speaking last week to a group of independent school headteachers, Mr Knight referred to the Government's "education and spills bill" - which suggests he used to work for the Department for Education and Spills. It explains a lot.