Charlotte-Mecklenburg Schools is among four districts a recent study identified as failing to keep enough great teachers and get rid of the weakest, Superintendent Heath Morrison said as he prepares to meet with principals next week.

Morrison plans to bring one of the authors of “The Irreplaceables,” a report on retaining highly effective teachers, to meet with principals. . The report by TNTP, a New York-based advocacy group formerly known as The New Teachers Project, urges districts to overcome “negligent retention” practices that make it difficult to keep star teachers and improve struggling schools.

“Negligent retention sends the dangerous message that great teachers are expendable and that anyone can make a career out of teaching, regardless of how well they perform,” the report says. “Tolerating poor performance keeps ineffective teachers in the classroom indefinitely, demoralizes outstanding teachers, and allows the entire teaching profession to be defined by mediocrity rather than excellence.”

Morrison, who became CMS superintendent this summer, said the study raises important questions for all principals: “What are the things that prompt people to leave the teaching field, and what can we do to make sure our highest performers want to stay? Am I doing things that contribute to my best talent walking out the door?”

The study, which has gotten national attention this summer, looked at “four large, geographically diverse urban school districts” with about 90,000 teachers combined.

“The districts weren’t identified and we don’t have to reveal ourselves, but why would we not?” said Morrison, who said knowing CMS was a source of data makes it more pressing to respond.

“The Irreplaceables” pushes a “smart retention” approach that includes strong emphasis on identifying the top 20 percent of effective teachers, remedying working conditions that drive them away and paying them “what they’re worth.” Districts should set a goal of retaining 90 percent of the identified teachers, the report says.

The plan also calls for creating baseline standards that identify ineffective teachers, removing policy barriers that keep them in classrooms and “encourag(ing) low performers to leave voluntarily by creating alternatives to formal dismissal.”

While the goal of identifying and encouraging top teachers is widely embraced, specific approaches tend to be controversial.

TNTP, which was founded by Michelle Rhee in 1997, initially focused on recruiting and training teachers without a traditional education background for hard-to-staff schools, an approach that some believe devalues experienced teachers and the work they did to prepare. The group worked with the Washington, D.C., public schools; Rhee was hired as chancellor of that system when the school board was stripped of its decision-making power.

Rhee spoke in Charlotte earlier this week at a forum promoting parent takeovers of low-performing schools. Mecklenburg ACTS, a local advocacy group, held a protest, saying her approach to education demoralizes teachers and overemphasizes standardized testing.

TNTP used “value-added” ratings based on student test scores to identify the most and least effective teachers in the four districts.

“While these measures cannot provide a complete picture of a teacher’s performance or ability on their own – and shouldn’t be the only measure used in real world teacher evaluations – they are the most practical way to identify trends in a study of this scale, and research has demonstrated that they show a relationship to other performance measures, such as classroom observations,” the report says.

When CMS launched value-added ratings in 2010, they sparked significant backlash. Many teachers were skeptical of the complex formulas that were supposed to calculate the teacher’s contribution to each student’s progress. And some parents complained that the dozens of new tests created to generate the ratings wasted classroom time.

CMS later scrapped its value-added ratings, but North Carolina is working toward a new version.

The district’s push to base teacher pay on effectiveness, rather than experience and credentials, has stalled, hobbled partly by controversy and partly by the recession. This year CMS leaders lobbied hard to provide a 3 percent across-the-board raise, the first most teachers had gotten in four years. The school board relies on the state legislature and county commissioners for teacher raises.

Morrison noted that many of the measures recommended in “The Irreplaceables” – such as giving teachers high-quality, rigorous feedback – don’t cost money.

“Let’s start off with the things we can control,” Morrison said.