The Home School Legal Defense Association (HSLDA) commissioned a study drawing data for the 2007-2008 school year from multiple standardized testing services, comparing homeschool students to public school students.   The national average percentile scores were higher in all subject areas by at least 34 percentile points, and as high as 39 percentile points.

ACT Testing

Also in recent years homeschool students have scored 1-2 points higher on the ACT test when compared to the national average, which includes students from both public and private schools.

Four grades higher

"Then the gap widens so rapidly that by the eighth grade, the average homeschooled student performs at four grade levels above the national average-that is, eighth-graders perform at the level of high school graduates. "  - Starks, Rodney 2012. America's Blessings: How Religion Benefits Everyone, Including Atheists. PA: Templeton Press. 74-75