Tracy Robinson was losing them. The lesson for her fourth-grade class at Cincinnati's Vine Elementary School on this Friday afternoon was fractions, and as she stood at the front of the room with her textbook, explaining why 1/3 is larger than 1/4, she saw blank stares. No hands were raised. She drew shapes on the blackboard, shading in parts of them, but that didn't work either. The kids were wiggling in their seats. "I was getting so nervous," Robinson recalls. "I was feeling like, 'O.K., now what do I do?'"
Despite their best efforts, American educators well know the sensation. New...