Building a better math teacher: some (surprising) research into teachers' disciplinary knowledge

There is a long-standing assumption that more effective mathematics teaching is linked to taking more courses in mathematics. Unfortunately, despite extensive efforts, there is virtually no proof to support this suspicion. That dearth of evidence has prompted researchers to reframe their investigation of the mathematics that is important to effective teaching -- and the emerging research challenges many of the structures and emphases that define most school mathematics curricula and most teacher preparation programs.