This article discusses quantitative research on homeschooling, including the available data, pitfalls of using the data, estimates of the number of homeschooled children, part-time homeschooling, and why families homeschool. I compare research on homeschooling to research on charter schools, voucher programs, and private schools.The number of homeschooled children is over 1 million, more than 2% of the total number of school children and roughly equal to the total in charter schools and voucher schools combined. There is approximately one homeschooled child for every five children enrolled in private school. 1 Despite its size, scarce data on homeschooling have impaired our understanding of even the most basic questions, including a precise