Online Learning > Face-to-Face Learning?

Yes, according to a U.S. Department of Education study.

From the study:

A systematic search of the research literature from 1996 through July 2008 identified more than a thousand empirical studies of online learning. The meta-analysis found that, on average, students in online learning conditions performed better than those receiving face-to-face instruction.

Potential effect(s) on K-12 education: uncertain. The following was in the study's abstract:

An unexpected finding was the small number of rigorous published studies contrasting online and face-to-face learning conditions for K–12 students. In light of this small corpus, caution is required in generalizing to the K–12 population 
because the results are derived for the most part from studies in other settings (e.g., medical training, higher education).

The New York Times wrote about the study in this August 19th article.