Rotten Apples

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For years, school systems across the country have considered making student performance a key factor in teacher evaluations. Now, one of the country's largest districts has found a compelling reason to do just that.

Researchers in Dallas have shown that having a less-than-effective teacher can significantly lower a student's performance over time, even if the student gets more competent teachers later on. Though that might not seem particularly surprising, district officials were struck by just how much teacher quality mattered to student achievement.

"This is the first time we've measured teachers' effects on the ability of kids to perform on assessments," says Robert Mendro, district director of institutional research. "And what surprised us the most was the size of the effect."

Building on the work of William Sanders, who has tracked the effects of teacher quality in Tennessee, Dallas researchers started by dividing about 1,500 of the district's 8,500 teachers—those for whom complete personnel information was available—into five groups of equal size, from least to most effective. Teachers' effectiveness was based on comparisons of their students' test results at the end of the year with those of students with similar backgrounds who were in the previous grade the year before. Teachers whose students made the greatest gains on the assessments—the Iowa Tests of Basic Skills and state tests—were deemed most effective. The researchers also took into account student background factors such as race, English proficiency, and poverty.

They then tracked the three-year progress of about 17,000 students who were in grades 4-8 by the 1995-96 school year. Those students who had more of the most effective teachers generally made far greater gains on the Iowa Tests than those who had less effective ones. For example, the average reading scores of a group of 6th graders who had three of the most effective teachers in a row rose from just under the 60th percentile to the 75th. A similar group of students who had two of the least effective teachers and then one of the most effective ones dropped from just above the 60th percentile to just below the 50th.

"What it does," Mendro says, "is send a message loud and clear that we've got to invest more in staff development, in getting teachers with more skills, and in retaining our best teachers."

Now that they have the data, district officials are looking at how to respond. Some school board members say the research bolsters their arguments that the system should consider giving student performance a more prominent role in teacher evaluation. "We want to see what happens when you really do link student performance with teacher evaluations and with accountability," says board member Kathleen Leos.

Currently, Dallas teachers are given "classroom effectiveness indices" based on how well their students perform on a battery of tests. But the indices aren't available until the summer, while the teachers' formal evaluations are in the spring. Some principals, nonetheless, use the indices. Judy Zimny, principal at Hotchkiss Elementary School, says she looks at teachers' effectiveness records when helping them set goals for the coming year. When the teachers' evaluations take place later in the spring, she tries to evaluate how well they've met their goals. "It's just one more piece," Zimny says, "though it's an especially relevant piece."

District officials say they hope the data will help principals identify teachers for additional professional development. "This is not a tool to eliminate teachers," says James Hughey, the district's acting superintendent. "It is a diagnostic tool to identify where the needs are." Still, he adds, "this is just in the talking stage."

Some experts warn against basing teachers' evaluations too much on their students' test scores. "One year of test scores is a pretty poor indicator," says Julia Koppich, an education consultant from San Francisco who has studied teacher evaluation systems. "You need two, three, or four years to get a pattern, and a poor teacher shouldn't need to wait that long to get help." Koppich favors peer-review systems in which teachers evaluate and mentor each other to improve quality.

In Dallas, meanwhile, some teachers worry that the district's findings could be used unfairly to tarnish educators' reputations. What's needed, they argue, is better support and working conditions. "My contention is that the preponderance of teachers across this nation and here in Dallas are good teachers," says Roy Kemble, president of the Classroom Teachers Association of Dallas, "and if you gave them a different working environment, they'd do better."

—Jeff Archer

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