The massive Measures of Effective Teaching Project is finding that teacher effectiveness assessments similar to those used in some district value-added systems aren't good at showing which differences are important between the most and least effective educators, and often totally misunderstand the "messy middle" that most teachers occupy. Yet the project's latest findings suggest more nuanced teacher tests, multiple classroom observations and even student feedback can all create a better picture of what effective teaching looks like.

Researchers dug into the latest wave of findings from the study of more than 3,000 classes for a standing-room-only ballroom at the American Educational Research Association's annual conference here on Saturday.

"The beauty of multiple measures isn't that there are more of them—more can be more confusing—these need to be alligned to the outcomes we care about," said Steve Cantrell, who oversees the MET project for the Bill & Melinda Gates Foundation. Existing teacher evaluation systems often use indicators that are not effective at guaging student achievement, and moreover that lump teachers into too-simplistic categories.

"The middle is a lot messier than a lot of state policies would lead us to believe," Cantrell said. "Teachers don't fall neatly into quartiles. Based on the practice data, if I look at the quartiles, all that separates the 25th and 75th on a class (observation) instrument is .68—less than 10 percent of the scale distribution. In a lot of systems, the 75th percentile teacher is considered a leader and the 25th percentile considered a laggard. ...This would suggest they're a lot closer than being off by two categories."

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