“The initiative itself tried to pull a bunch of levers to have a big impact on student performance,” said Brian Stecher, a RAND researcher and the lead author of the report. “The sites did in fact modify all of these levers, some more than others, but in the end, there were no big payoffs in terms of improved graduation [rates] or achievement of students in general, and low-income and minority students in particular.”

That was the conclusion of a study paid for by the Gates Foundation, into their own Teacher Evaluation/Merit Pay experiment or "The Intensive Partnerships for Effective Teaching initiative", which cost $575 million in total.

From this comes the following recommendations

Reformers should not underestimate the resistance that could arise if changes to teacher-evaluation systems have major negative consequences for staff employment.
A near-exclusive focus on TE might be insufficient to dramatically improve student outcomes. Many other factors might need to be addressed, ranging from early childhood education, to students' social and emotional competencies, to the school learning environment, to family support. Dramatic improvement in outcomes, particularly for LIM students, will likely require attention to many of these factors as well.

One of the recommendations should have been to listen to teachers. Over and over again, teachers warned that high stakes evaluations ties to student achievement would not only fail to produce the hoped for results, but would have serious negative consequences on students (over-testing) and teacher.

Imagine if Gates would have spent his fortune on some of the items listed in the second bullet point, instead of listening to corporate education reformers and their desire to test and punish.