Apollo became a premier growth company by catering to working adults' almost insatiable demand for higher education. Enrollment at its University of Phoenix (UOP) and other schools surged 28% in 2003. Even as the Phoenix-based company's UOP continues its march to become truly national, Nelson is tapping into the even-greater demand for online education. Web enrollment is up 60%, to 91,000 students, over the past year. Nelson is exploiting economies of scale to drive up margins. The payoff: Profits rose at an average annual 52.1% rate for the past three years.