The community of K-12 education has seen explosive growth over the last decade in distance learning programs, defined as learning experiences in which students and instructors are separated by space and/or time. While elementary and secondary students have learned through the use of electronic distance learning systems since the 1930s, the development of online distance learning schools is a relatively new phenomenon. Online virtual schools may be ideally suited to meet the needs of stakeholders calling for school choice, high school reform, and workforce preparation in 21st century skills. The growth in the numbers of students learning online and the importance of online learning as a solution to educational challenges has increased the need to study more closely the factors that affect student learning in virtual schooling environments. This meta-analysis is a statistical review of 116 effect sizes from 14 web-delivered K-12 distance education programs studied between 1999 and 2004. The analysis shows that distance education can have the same effect on measures of student academic achievement when compared to traditional instruction. The study-weighted mean effect size across all outcomes was -0.028 with a 95 percent confidence interval from 0.060 to -0.116, indicating no significant difference in performance between students who participated in online programs and those who were taught in face-to-face classrooms. No factors were found to be related to significant positive or negative effects. The factors that were tested included academic content area, grade level of the students, role of the distance learning program, role of the instructor, length of the program, type of school, frequency of the distance learning experience, pacing of instruction, timing of instruction, instructor preparation and experience in distance education, and the setting of the students. Appended is: Coded Variables and Study Features in the Codebook.