Mayor Michael Bloomberg’s testimony before an arbitrator drove one nail into the coffin of the city’s plans to replace or rehire teachers at 24 “turnaround” schools.

Last week an arbitrator determined that the city violated the city’s contracts with the teachers and principals unions when it moved to replace staff members at the schools. This afternoon the arbitrator, Scott Buchheit, released a detailed explanation of why he ruled the way he did.

The city was trying to use hiring procedures set for closing schools and their replacements. But the unions argued that the turnaround plans were “sham closures” that would not result in new schools. Instead, they argued, the city was unfairly using contractual provisions about “excessing” to remove teachers and administrators it deemed unsatisfactory.

In upholding the unions’ grievance, Buchheit at times turns Bloomberg’s and other city officials’ words against them.

He quotes a 2011 memorandum written by the Department of Education’s chief financial officer, which said, “excessing is not a permissible way to deal with unsatisfactory teachers.”

Yet city officials said they intended to do just that from the start of the turnaround process, Buchheit determined.

When he first announced the turnaround plans during his State of the City Address in January, Bloomberg “repeatedly made clear that the DOE’s new plan concerning the 24 (then 33) schools was based upon the desire to change staffing in the classroom,” Buchheit writes. He quotes Bloomberg saying, “Under this process, the best teachers stay; the least effective go.”

The arbitrator notes that Bloomberg has frequently expressed his distaste for the current process for shedding teachers from schools that are contracting, which is based on seniority, not job performance. “Suffice it to say that at the arbitration hearing the Mayor reaffirmed his dislike,” Buchheit writes.

Buchheit emphasized that he was not passing judgment on the value of the city’s plans for the schools, which State Education Commissioner John King approved in late June. And he said nothing in his decision would prevent the city from continuing with portions of the plans that do not involve using the hiring rules that take effect when schools are closed.

Those rules, outlined in a clause in the teachers union contract known as 18D, call for closing schools to set up hiring committees to review current teachers who apply for jobs at the replacement schools. According to 18D, the committees must hire back at least half of them of the qualified applicants from each school. City officials and school administrators began carrying out 18D procedures in the 24 schools last month with the understanding that the arbitrator could ultimately reverse it.

Department of Education officials had said they were confident that King’s approval of the reform plans would prove that the 24 schools were truly being closed. But Buchheit said King’s decision did not necessarily mean the schools were being closed and replaced with new schools. “New,” he said, typically means “never existing before,” which would not be the case for the 24 schools.

“The evidence here establishes that much would remain the same in the 24 new schools,” he wrote, including the schools’ buildings, student populations, courses, partnering organizations, and, for 18 of them, their principals. He also noted that many of the schools’ new names would still contain the old names, such as August Martin High School, which would change to “The School of Opportunities at the August Martin Campus.”

Deputy Chancellor Marc Sternberg also suggested that the school closings were inauthentic, the arbitrator concludes, when he wrote in a memorandum to principals shortly after Bloomberg’s speech explaining that their schools would be closed “as a technical matter.”

For the schools to be truly new, Buchheit says, much would have to change, including their overall educational visions and leadership. Instead, the biggest change the city cited was the planned staffing change — but that change could only happen, he notes, if the schools were new.

“The DOE cannot use the end result of Article 18D being invoked as justification for why it is permitted to invoke 18D,” Buchheit writes. “I cannot adopt this circular reasoning for the purposes of contract interpretation.”

On Monday, Bloomberg said the city would appeal Buchheit’s ruling because the arbitrator had not yet explained his rationale. But after reading the opinion, city attorney Georgia Pestana said the city will not withdraw its appeal, which it filed in State Supreme Court on Monday. “The arbitrator clearly exceeded his authority,” she said.

The city had argued that the unions’ grievances were not arbitrable at all. In his opinion, Buchheit rejects each of the city’s three arguments for why the grievance should not be subject to binding arbitration.

Buchheit’s full decision is below: