As hundreds of D.C. teachers await annual evaluations that could trigger their dismissals this month, attorneys for the District and the local teachers union are battling in court over what parts of the performance appraisal, if any, can be legally challenged.

The case, pending before D.C. Superior Court Judge Anita M. Josey-Herring, is the first skirmish in what is likely to be a protracted legal war waged by the Washington Teachers’ Union to contest the rigorous evaluation system known as IMPACT. A central initiative of former chancellor Michelle A. Rhee, it led to the firing of 126 teachers last year and could result in the dismissals of as many as 600 this summer.

Before Rhee’s 2007 appointment, firings for poor performance were exceedingly rare. Rhee resigned in October and was replaced by her deputy, Kaya Henderson.

The District went to court in February to block union efforts to contest firings before an independent arbitrator. Attorneys for the city contend that District law and the labor contract approved last year prohibit arbitration, which the union has used with some success to challenge recent terminations.

Josey-Herring ruled on June 8 that the union could seek arbitration to contest procedural errors in evaluations but not the substance of IMPACT or the ratings instructors receive. She asked attorneys from both sides to collaborate on drafting an order she can sign. The order is due at the end of next week, but union sources say there is a strong likelihood that the union will appeal.

Similar legal disputes are unfolding across the country as cities and states attempt to toughen evaluations by holding teachers more accountable for raising student achievement. Last month, the New York state teachers union sued the Board of Regents — the state’s top education policymaking body — charging that it exceeded its authority by allowing school districts to base 40 percent of teacher evaluations on test scores. An attempt by Los Angeles teachers to block a new evaluation plan was recently rejected by California.

D.C. school officials have hinged much of their effort to improve schools on raising the quality of the city’s 4,200-member teacher corps. Citing research that identifies teachers as the dominant in-school factor driving growth on standardized test scores, they have invested millions of dollars in IMPACT to help remove subpar instructors and improve the performance of others.

Union leaders and many teachers regard the system, in its second year, as arbitrary and punitive. They assert that IMPACT does little to help develop them professionally and makes little allowance for school or classroom conditions that can interfere with instruction and lower evaluation ratings.

Union president Nathan Saunders, who unseated predecessor George Parker last fall largely on the strength of rank-and-file unhappiness with IMPACT, has vowed to force significant changes in the system.

“We will be exerting constant pressure until we have a fair teacher evaluation system,” Saunders said.

Henderson did not respond to a request for comment.

Under IMPACT, teachers are observed in their classrooms by principals and independent “master educators” five times over the course of a school year. They are assessed primarily for their compliance to nine broad standards, including ability to explain content clearly, to engage students with varied skill levels, maximize instructional time and check for higher-level understanding through skilled questioning. About 450 teachers, working in grades in which the annual D.C. Comprehensive Assessment System tests are given, have half of their evaluation determined by whether student scores meet growth benchmarks.

In the 2009-10 school year, when IMPACT debuted, almost 70 percent of teachers (2,892) scored in the “effective” range. About 16 percent (663) were rated “highly effective,” making them eligible for performance bonuses of up to $25,000. Less than 2 percent (72) were deemed “ineffective” and dismissed. Another 13 percent (568) were found to be ”minimally effective.” Of those, a small number had their jobs eliminated last year for budget or enrollment reasons. The rest are subject to termination this month if they receive the same rating.

Critics cite the location of top-rated teachers as evidence that IMPACT disadvantages instructors in schools with high rates of poverty and other social problems. Just 5 percent of the “highly effective” teachers work in Ward 8, the city’s most impoverished area, while 22 percent are in Ward 3, the most prosperous.

The legal dispute began in November, when the union filed a class-action grievance asking that the 2010 dismissals and “highly ineffective” designations go before an arbitrator. The union contended that IMPACT set unclear expectations for teachers and was based on arbitrary and capricious scoring. It also charged that there was a lack of transparency in the city’s calculation of “value-added” data used to measure student growth on test scores.

The union asked for elimination of all negative evaluation scores and reinstatement of terminated teachers.

The District sued to block the arbitration request, citing a provision of D.C. law that exempts teacher evaluations from collective bargaining. Congress granted the power in the mid-1990s after the union refused to negotiate the then-existing evaluation system with the District. While other school systems have bargained the details of evaluations with unions, Rhee had the power to effectively impose IMPACT on D.C. teachers.

District attorneys argued that because IMPACT wasn’t subject to collective bargaining, grievances growing out of it are not subject to arbitration. They also cite a provision in D.C. law that allows teachers to appeal a poor evaluation to the chancellor and the city’s Office of Employee Appeals.

Saunders and union attorneys said the appeals agency is toothless and takes years to process cases. They also cited grievances involving the school system’s previous evaluation systems that went to arbitration.

Arbitration has historically been a friendlier forum for unions, and teachers have enjoyed some limited success in challenging District actions. In February, arbitrator Charles Feigenbaum ordered the District to reinstate 75 probationary teachers fired by Rhee in 2008. He deemed the dismissals improper because the teachers were not told why they were let go. The District is appealing the ruling.