Curriculum suppliers, state departments of education, and home school leaders, are the sources used to estimate that between 248,500 and 353,500 school-aged children (K-12) were educated at home in the 1990-91 school year. This paper explains how this estimate was derived. It provides information on process, possible bias, alternate survey collection of data, and why the three methods were chosen. In the estimates reported, most adjustments to actual data were based on a survey of a sample of the membership of the Home School Legal Defense Association. In deriving figures for the first method, a survey of 16 suppliers of curricular packages yielded an estimate of between 309,000 and 353,500 K-12 children who are educated at home. For the second method, 37 state departments of education reported 82,061 children for whom parents have filed papers with state or local officials, representing a fraction of the total. For the third method, information from 25 home schooling leaders in 17 states yielded a national estimate of between 248,500 and 304,000. A brief analysis of recent trends with a conclusion is given. Appended are home school data collected by states, information from associations, and a summary of selected research reports from two state departments of education. (RR)