The increasing prevalence of private tutoring has received minimal scholarly attention in the United States. We use over 25 years of geocoded data on the universe of U.S. private tutoring centers to estimate the size and growth of this industry and to identify predictors of tutoring center locations. We document four important facts. First, from 1997 to 2022, the number of centers more than tripled, from about 3,000 to 10,000, with steady growth through 2015 before a more recent plateau. Second, the location and growth of private tutoring is heavily concentrated in areas with high income and parental education. More than half of tutoring centers are in areas in the top quintile of income. Third, even conditional on income and parental education, private tutoring centers tend to locate in areas with many Asian American families, suggesting differences in demand by ethnic or cultural identity. Fourth, we see only marginal evidence that the private tutoring market tracks K-12 school markets, i.e. charter, magnet, or private school options. The rapid rise in high-income families' demand for this form of private educational investment mimics phenomena observed in other spheres of education and family life, with potentially important implications for inequality in student outcomes.