Missing Links: The 4 Concepts To Help Close the Gap

Recent studies show that once American students reach middle school, they begin to fall behind the students of many other countries in mathematical understanding and achievement. Learner.Org has put together great professional development videos that focus on the 4 concepts that the TIMSS testing shows areas of weakness. Master teachers lead the videos which are broken down into 8 workshops.
Note: you will need to register (free) in order to watch the video on demand (VOD). You can also order the guides and the videos. I found the videos highly enlightening.