Normally, Sherry Geesaman wouldn’t be nervous. Normally, she’d flip open a plan book or a textbook and start riffing. That is, after all, what veteran educators do. And Geesaman’s been teaching for 20 ...

A correction to an earlier version of this article has been appended to the end of the article. When Veera Sinha was a little girl in India, her father asked his kids to solve math puzzles in their ...