Spaced Education.

SpacedEd is a learning environment that focuses on using questions to facilitate the learning of content.

From the Website:

It is based upon two core psychology research findings: the spacing effect and the testing effect. In more than 10 randomized trials completed to date, spaced education has been found to:

• Improve knowledge acquisition;
• Increase long-term knowledge retention (out to 2 years);
• Change behavior; and
• Boost learners' abilities to accurately self-assess their knowledge.

The system sends questions to e-mail two times a day. If the questions are answered incorrectly they are redelivered after a week. I'm currently testing it out on the "Philosophy" class which focuses on the philosophy of education. I've only answered two questions, but have already started to see some potential use for the classroom (especially if SMS is allowed.)