The growing phenomenon of private tutoring has received minimal scholarly attention in the United States. We use 20 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 1997-2016, the number of private tutoring centers grew steadily and rapidly, more than tripling from about 3,000 to nearly 10,000. Second, the number and growth of private tutoring centers is heavily concentrated in geographic areas with high income and parental education. Nearly 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 immigrant and Asian-American families, suggesting important differences by nationality and ethnicity in demand for such services. Fourth, we see little evidence that prevalence of private tutoring centers is related to the structure of K-12 school markets, including the prevalence of private schools and charter or magnet 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.