I knew I'd made it when ...

• Name: Rohit Agarwal
• Company: TenMarks, San Francisco

We started TenMarks to address the fact that U.S. math scores are abysmal compared to other developed nations. We reinforce math concepts taught in school by offering online courses for students who are struggling.

We launched the product in December 2010 for teachers. It was a very soft launch: We just told about 50 teachers and a few bloggers. Our goal was to get 500 teachers using it. But an education blogger picked up the story, and by January we had 11,000 classrooms using the program.

We weren't prepared for the success. Our team was putting band-aids on the servers every night to help handle the traffic. But we realized that we'd identified a core problem that needed to be solved, and our product really seemed to resonate. Now we have 25,000 schools on board in some of the largest districts in the country.

NEXT: We were cash-flow positive in three weeks