The big shoe ready to drop this summer on the DCPS labor relations front involves the estimated 550 teachers who are subject to dismissal if they receive a second consecutive “minimally effective” rating on the IMPACT evaluation system. For Mayor Vincent C. Gray and Acting Chancellor Kaya Henderson, it will be a closely watched test of their resolve to follow through on a signature initiative of the Michelle Rhee era, designed to improve teacher effectiveness by pushing poor performers out of the system.

It now appears that some teachers — most likely younger ones — will get a reprieve from the two-strikes-and-out rule established in 2009. Earlier this week, human capital chief and IMPACT architect Jason Kamras told principals that if they had young teachers with promise who were headed for a second poor evaluation, they could apply for exceptions.

“We recognize that in some cases, a principal might want to retain a second-year teacher who has received minimally effective ratings in each of his or her first two years of teaching but has demonstrated improvement and the potential to become an effective teacher in the following year,” Kamras said.

“You know your teachers best, so we would like your recommendation on whether a new teacher in your building should receive an exception. If you would like to retain such an individual, please write a letter explaining why this individual should receive an exception to the separation policy.”

Kamras said in an e-mail Friday that there is “a sound, research-based justification” for exceptions.

“A wide body of education research indicates that the learning curve for new teachers is quite steep. The policy you cite above is an effort to take this into account. If a principal can demonstrate that a twice-Minimally Effective teacher has shown significant growth in her/his first two years in the profession and is likely to become Effective or Highly Effective the following year, we will consider granting the teacher an additional year to improve. Teachers at later points in their careers, however, are expected to be beyond the steep portion of the learning curve.”

Kamras said Henderson will make final decisions by July 15.

This is unlikely to sit well with older teachers, many of whom already believe that Rhee and Henderson see IMPACT as a means to usher them out in favor of younger recruits from alternative training programs whose alumni are heavily embedded in DCPS management: Teach for America and D.C. Teaching Fellows. Henderson — like Kamras and Rhee, a TFA vet — may well get a question or two about this at her confirmation hearing next week from council members wondering why the rules are being changed in the middle of the game.