“If you don’t get mathematics to the highest level you possibly can in high school, your career options shrink dramatically in the 21st century,” Mr. Compton said. “Our society basically tells girls they’re not good at math. I was determined that was not going to happen to my daughters.”

Mr. Compton and Indian Math Online’s co-founder, Suresh Murthy, hired a team of math teachers and software developers in India to build the site and its curriculum. At first, the site was meant for their daughters, but soon friends started asking if they could use it and word gradually spread. It has lessons for students in grades one through 12 and offers several packages for $12.50 to $20 a month.

Two-thirds of the students using it are children of Indian and Chinese immigrants. Mr. Murthy’s children are an example. “He grew up in India, and he worried about his daughters falling behind in the global competition to be educated for the 21st century,” Mr. Compton said.

The site’s curriculum is