ROCHESTER, N.Y. — Jennifer Craig stared at her daughter’s fifth-grade math homework. It was a three-digit multiplication problem, and it seemed simple enough. But her 10-year-old was supposed to solve it by drawing a chart, breaking apart numbers, multiplying, adding and maybe more. “I’m lost,” said Craig, a 31-year-old stay at home mother of three. And that’s how she found herself in her daughter’s classroom Monday night, sitting alongside other parents in child-size chairs and listening as teacher Alyshia Thomas explained new math strategies. Most U.S. public school students are learning math very differently than their parents did, due to...