TAMPA — After six years of effort, high hopes and more than $180 million spent, the Hillsborough County school system is unraveling the teacher evaluation system it developed with the Bill & Melinda Gates Foundation.

The news came in an email this week from superintendent Jeff Eakins to more than 260 "peer evaluators" and mentors who form the core of the system.

It also arrived as the once-cordial relationship between the district and its teachers union imploded Thursday. The two sides walked away from each other in anger as talks over a salary agreement for the current school year broke down.

Eakins announced in his email he has formed a committee to transition away from the once-touted Gates program, and said a number of employee groups would be on the panel.

Unlike the complex system of evaluations and teacher encouragement that cost more than $100 million to develop and would have cost an estimated $52 million a year to sustain, Hillsborough will likely move to a structure that has the strongest teachers helping others at their schools.

Eakins said he envisions a new program featuring less judgemental "non-evaluative feedback" from colleagues and more "job-embedded professional development," which is training undertaken in the classroom during the teacher work day rather than in special sessions requiring time away from school. He said in his letter that these elements were supported by "the latest research."

That's a radical departure from the classroom observations carried out by full-time evaluators who rated the teachers according to a rubric, or scorecard. Bill Gates, the founder of Microsoft, and his wife Melinda funded the project and others in U.S. cities through their philanthropic organization.

They hoped the system would create a hierarchy of teachers who could be paid based on their skills. Struggling teachers would be given assistance or, in the worst cases, fired or counseled out of the profession.

The foundation was expected to contribute $100 million through 2016, but instead paid $80 million. It is unclear to what extent the organization will continue to be involved in Hillsborough or whether it will forward any more money to the district.

The school district, meanwhile, has spent well beyond the $100 million it pledged, although some of the money was for related projects including a principal training program.

READ MORE: How Hillsborough County's Gates grant became a budget buster

Among the selling points Hillsborough made back in 2009 when securing the Gates foundation's support: a close working relationship between district officials and the Hillsborough Classroom Teachers Association. District leaders praised and promoted the union at public gatherings, and assured teachers that members were equal partners in designing the system.

The Gateses hoped the newly developed systems in Hillsborough and elsewhere would result in all students — especially those with the highest needs — getting quality teachers.

But in a report published Sunday, the Tampa Bay Times showed the project fell short of many of its goals and cost more to sustain than the district could afford.

Lower-income schools continue to hire the newest and least qualified teachers. Test scores are still measurably lower for poor and minority students. And Hillsborough's graduation rate now lags behind other large counties in Florida.

As it rolled out the Gates-funded system, the district agreed to a new pay plan for teachers that added $65 million a year to payroll costs. That amount does not include more than $12 million in performance bonuses, which are now required by state law.

Despite those costs, which were revealed during the summer, the teachers union entered this year's negotiations with hopes of getting raises for teachers and classroom aides, who earn as little as $9.12 an hour.

Negotiations were suspended as district officials grappled with news that they were spending down too much of their reserves.

When talks finally resumed, the union asked for support workers' hourly wages to increase in three phases until they started at $10.77. For teachers, the union wanted everyone to advance a pay year and get an additional $1,000. For the highest-paid employees, the union asked for a 2 percent bonus.

Both sides described the proposal as a first step.

But Thursday's bargaining session was over almost as soon as it began. Mark West, the district's employee relations manager, said because of the district's budget difficulties, he would have little to offer anyone, including the support employees.

"I'm glad you're comfortable leaving your employees living in poverty," union executive director Stephanie Baxter-Jenkins shot back.

"I'm not saying I'm comfortable," West said.

Not long after, Baxter-Jenkins told the district's team, "You might as well just go."

While West spoke of the district's financial difficulties, Eakins did not mention money in his email about the Gates program.

Instead, he cited new research that suggests it is better for teachers to help one another than to mark each other down on scorecards.

"By bridging current research with the knowledge gained from the last six years, we will build an even stronger support model for our students and teachers," he wrote.

"Specifically, this transition will enable highly effective teachers to sharpen their teaching skills as they work directly with students every day. … Both teachers and students will benefit from the collegial relationships that develop over time."

Eakins did not mention the Gates situation, or the Times report, in a four-hour televised School Board meeting Tuesday. But in his email, he said "newspaper articles, social media and the general buzz" around the Gates grant had moved him to address the peer evaluators.

He drew on his own years as an elementary school teacher to praise those who took part in the experiment.

"My peers challenged me to reflect on my practice and provided indispensable guidance starting on my very first day in the classroom and continuing throughout my teaching career," he wrote.

Contact Marlene Sokol at (813) 226-3356 or msokol@tampabay.com. Follow @marlenesokol.