Like educators across the city, Mark Anderson is back in the classroom today. But it’s not the one he left in June.

Anderson chose to look for a new school after two years as a special education teacher at a struggling Bronx elementary school. In the Community section today, he explains what motivated his move — and argues that administrators at schools like the one he left could stem their annual teacher exodus just by being nice.

Anderson writes:

I can’t say that I am an “irreplaceable” teacher. But I do know that some of the teachers that I have worked with are, and that we have chosen to forsake our school.

The education policy group TNTP coined that term this summer in a report that calls for changes to teacher retention policies. The top 20 percent of teachers are “irreplaceables,” TNTP concluded, and yet they must be replaced far too often. Like many educators, I may take issue with some of the flashpoints of TNTP’s report — the aggrandizing term of “irreplaceable,” the focus on firing “low performers,” the notion of merit pay, or the idea that the wheat can even be separated from the chaff given the measures that currently exist.

But … the report got one critical point right: most teachers depart due to a failure in school leadership. As the report further notes (under “low-cost retention strategies”), the remedy for this failure can be heartrendingly easy: All it would often take to retain some effective teachers is a few positive words of recognition.

Not only were words of recognition absent at his old school, but teachers who should have been praised were criticized while teachers who declined to make the extra effort escaped censure, Anderson writes. The dynamic is reversed in his new school, he reports.