http://www.ted.com/talks/lang/eng/bill_gates_unplugged.html
In summary, currently teachers are not held accountable for the quality of their teaching due to the way their contracts are structured. Also, formulas for teacher's pay reward experience and extra education, even though both have been shown to be unrelated to teaching quality.
Simply throwing more money at the problem will not help, we need to rethink the current system.