A new study finds that it doesn't take long to recognize the best and worst teachers. It found that overall teacher effectiveness improves dramatically during the first two to three years of teaching, but that relative effectiveness of individual teachers changes little over the years.
Teachers ranked in the lowest 20 percent of teachers during their first two years of teaching proved likely to be in that same bracket five years later. And teachers whose scores placed them in the top 20 percent of teachers in the study were even more likely to stay in that top bracket, said the study conducted for the National Center for Analysis of Longitudinal Data in Educational Research.
Data from 65,000 to 80,000 students in each grade was used for the study, which followed teachers who stayed in the teaching profession five years or longer. The teachers received value-added scores each school year, based on how well their students performed.
Value-added evaluation is a statistical way of judging teachers by comparing their students' test scores from the current school year to scores of those same students in the previous year, and to scores of similar students from a larger sample, said Allison Atteberry, one of the paper's authors. The goal is to isolate a teacher's contribution to a student's progress from other effects on school performance, such as poverty and parental involvement.
"A lot of information is brought to bear to make a good guess at how a kid would have performed with an average teacher," Atteberry said. "Getting that right is at the heart of a good value-added model."
Atteberry was surprised by the predictive strength of the value-added testing used in the study because forecasting teacher success has been a hard nut for researchers to crack, she said.
Many of the likely predictors that a teacher will be successful don't hold up under statistical scrutiny. Atteberry said that whether a teacher did undergraduate work at a competitive school doesn't predict success reliably, and neither does the preparatory pathway a teacher took into the profession — whether through a traditional college program or by an alternative route from another profession. A teacher's SAT scores or credentialing scores aren't strongly predictive of future success, either, Atteberry said.
An administrator's gut feeling about how effective a teacher is likely to become might be superior to any of those indicators, but it's a hard thing to quantify on paper.
"I think there are probably people in the field of teaching who do have a strong, clear predictive sense of how teachers will serve students, but it's difficult to leverage that for a large-scale policy," Atteberry said. "This study is about figuring out what we can learn from data to help us have some of those same kinds of insights."
Value-added measurements of teacher effectiveness are controversial, especially if they are used as the sole basis of teacher evaluation. A resource guide from the National Educators Association said value-added models should not be the principal basis for making high-stakes decisions about pay or tenure of teachers. There is lack of consensus among researchers about whether such measures accurately isolate the effects of a single teacher, the report said.
Results can be skewed because student achievement is influenced by many factors beyond a teacher's control, and students are not necessarily assigned to teachers on a random basis, which compromises the results. NEA recommends that teachers be evaluated by multiple measures, which could include classroom observations, student portfolios and test results. The NEA considers value-added measurements to be acceptable when used as part of a multiple-measure approach.
A 2012 study about teacher retention, "The Irreplaceables," found that of 90,000 teachers studied in four large, diverse urban school districts, about 20 percent are "Irreplaceables" — teachers who are so successful that they are almost impossible to replace. It's a number that happens to correlate to the upper 20 percent bracket in Atteberry's study — the teachers who start out strongest and stay strongest.
"Knowing the power of great teachers, one would expect schools to be sharply focused on keeping far more of their best teachers than their lower performers," a summary of the study said. "Instead, they retain all teachers at strikingly similar rates: and about half of all Irreplaceables leave within their first five years."
Reasons cited in the study include principals who make too little effort to retain their best teachers or remove low-performing teachers, and policies that give principals and district leaders few incentives to change their ways.
That study suggested that retaining top teachers should be a major priority for school systems. To do that, improve working conditions in schools, pay the best teachers what they are worth, and protect them during lay-offs, it said.
It's important for schools districts to implement meaningful teacher evaluation systems that are rigorous across multiple measurements, said Michael Hansen, an education researcher at the American Institutes for Research.
"If an evaluation system doesn't have any teeth, or if it's poorly implemented — just checking boxes rather than having meaningful information for decisions to be based on — that really has the potential to undermine the school system altogether," Hansen said.
Documenting poor teacher performance is a critical area of failure, Hansen said, especially in high-need schools.
"In those schools, you often have a revolving door of principals, and of leadership for interventions," he said. "If want to remove a poor performer, you need to document for two or three years. It just doesn’t happen in many school districts."
Identifying those poor teachers quickly, while their hiring is still probationary, is a simpler process, and that's one of the areas in which Atteberry's new study about early career teachers could make a difference.
She cautioned, though, that conclusions of the study she co-authored should be implemented carefully. In her study, the teachers who failed to improve belonged to a specific group — fourth- and fifth-grade teachers in New York City under a certain set of circumstances. The limits of the study don't prove inconclusively that teacher effectiveness is predictable, she said.
"I don't want to say that these teachers couldn't improve under other circumstances — had they been supported differently, had different training, been assigned to different schools. You have to be careful in using this during personnel decisions," she said.
Atteberry said the paper is the first part of a larger project that is still under way — one that will look even harder at who improves and who doesn't, and tries to figure out why.