Student test scores can identify effective teachers, new study says
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Student standardized test scores can accurately identify effective teachers, along with other performance measures such as classroom observations and pupil surveys, according to a major national study released Tuesday.
The study of 3,000 teachers in seven school districts by the Bill & Melinda Gates Foundation found that the controversial method of measuring student academic growth, known as value-added, was a valid indicator of how well teachers helped boost their students’ achievement over time.
As school districts across the country move to improve what is commonly viewed as ineffective teacher evaluation systems, the Gates study may accelerate the use of value-added, along with other measures of teacher performance.
That method, which calculates student academic growth after controlling for income, English ability and other factors outside an instructor’s control, has been criticized as invalid by many teacher unions and some researchers. They argue that the method cannot accurately isolate a teacher’s effect on student learning from other factors, such as disruptive classrooms.
But the Gates study found that teachers who were highly rated with their regular classes performed equally well when students were randomly assigned to other classrooms the following year. The study was the first large-scale research project to demonstrate, using random assignment, which teachers best increased student academic growth based on their own effectiveness, rather than on the type of pupil they have.
“The message is that value-added seems to do a good job sorting out what is a teacher’s contribution versus what kind of student you have,” said Dan Goldhaber, director of the Center for Education Data and Research at the University of Washington. “The report affirms that value-added is a useful tool -- not alone, but in conjunction with other means of assessing teachers.”
Grappling with the sticky question of how much to count test scores, the study recommended between half to one-third of a teacher’s evaluation.
The study also found that classroom observations were more reliable when performed by more than one person. But student surveys turned out to be even more accurate in predicting teacher effectiveness than observations by professional evaluators, the study found.
In a conference call, participants in the Gates’ Measures of Effective Teaching project emphasized that a balanced approach using several measures in evaluating teachers was best, and that the purpose was to help teachers improve -- not nail them for poor performance.
“If we want students to learn more, teachers must become students of their own teaching,” said Tom Kane, a Harvard University professor of education and economics who led the project. “This is not about accountability. It’s about providing feedback every professional needs to strive toward excellence.“
The report affirms the thrust of the new teacher evaluation system being developed in the Los Angeles Unified School District, according to Supt. John Deasy. Over the last two years, the district has unveiled a new classroom observation system, a student achievement measure called Academic Growth Over Time and new pupil and parent surveys.
Deasy will not issue his recommendations for how much each component should count until later this month. But he said Tuesday that the Gates report has “strengthened” his proclivity toward counting test scores for about 30% of the evaluation, with observations making up the greatest share.
-- Teresa Watanabe