Mayor Bill de Blasio defended New York’s tenure system on Wednesday, calling it an effective way to recruit and retain teachers one day after a California judge struck down a slate of laws related to job protections for teachers in that state.

“The tenure system, done right, is a valuable piece of the way we educate because what it’s going to allow us to do is get quality teachers, get them to stay in our school system,” de Blasio said at a press conference on Wednesday.

The comments come after a preliminary decision in Vergara v. California ruled that the state’s tenure law discriminates against poor and minority students, who get saddled with the most ineffective teachers whose jobs are protected under the law. Buoyed by the ruling, some advocates have already expressed interest in pursuing legal action against New York’s tenure law, which includes similar protections to those that teachers receive in California.

De Blasio said he had not reviewed the case, which has received national attention because of the implications it could have for other states with powerful labor laws. But he defended New York City as already having a “very aggressive process” in place to usher weak teachers out of the city school system.

Part of that process is a tenure review that in New York City has grown increasingly rigorous in recent years. Research from Stanford and the University of Virginia, released Wednesday, found that the city’s tenure review process has recently been effective at easing out ineffective teachers before they received tenure.

Five years ago, the city established a rubric to evaluate teachers up for tenure, a step that shifted the review process from the relatively pro forma exercise it had been for decades before. Tenure approval rates fall dramatically. Between 2007 and 2013, the percent of eligible teachers who received tenure fell from 97 percent to 53 percent.

Most of those teachers weren’t denied tenure, but instead had their decisions delayed: between 2008 and 2012, teachers whose probationary period was extended grew from less than 5 percent to over 40 percent of eligible teachers.

ercentage of New York City teachers who had tenure denied or extended, 2006-2013
Percentage of New York City teachers who had tenure denied or extended, 2006-2013

Researchers found that teachers who had their tenure decision delayed were 50 percent more likely to leave their school for another school the next year, and 66 percent more likely to leave the system altogether. And the teachers who replaced them typically scored better in their tenure reviews and showed some evidence of doing more to improve student test scores, they found.

Those teachers were more likely to work in schools with higher proportions of black students, the study found, which means the city’s tenure process has been “helpful to kids in those schools,” said the University of Virginia’s James Wyckoff, one of paper’s authors.

That is one difference between California’s tenure process and what happens in New York City, Wyckoff said. Whereas the judge viewed tenure in California as coming at the expense of students, Wyckoff said, “I think the approach the city is taking is that it wants to make sure teachers who receive tenure are effective.”

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