For all the difficulty of doing a rigorous evaluation in order to improve teaching performance across the board, I suspect it is a whole lot easier to identify the worst teachers in the school.

FORBES: Getting Rid of Bad Teachers

The foundation and others have estimated that it could cost between 1.5% and 2% of the overall budget for teacher compensation and benefits to implement a feedback and evaluation system based on multiple measures of teaching performance.

CNN: Bill Gates: Invest in better teaching

Improving the quality of teaching in the classroom by improving the preparation, professional development, and evaluation of teachers and principals.

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Starting in 2009, the Gates Foundation supported a project known as the Measure of Effective Teaching, or MET, which worked with 3, 000 teachers to come up an evaluation and feedback system that helped teachers improve.

FORBES: Bill Gates Says There Is Something Perverse In College Ratings