The National Association of Head Teachers walked out of the "social partnership" in 2005, arguing that schools were not adequately funded to pay for the compulsory planning, preparation and assessment (PPA) time that the partnership had helped introduce.
It joined the country's largest teachers' union, the National Union of Teachers, out in the cold.
Relations soured with other unions, who remained in the partnership and with the Government, which stopped sending ministers to NAHT functions.
But on Wednesday, 160 delegates attended a NAHT special general meeting in London, where 85 per cent voted to rejoin. The NAHT has won an agreement from the DfES that it will review funding of PPA time.
The union still faces hurdles before it can rejoin: other members of the social partnership, notably Chris Keates, the general secretary of the NASUWT teachers' union, wants assurances that the NAHT will abide by collective responsibility and will meet next month to decide on its readmittance.
Mick Brookes, who was elected as NAHT general secretary last year off the back of a campaign to leave the social partnership, had argued for the about-turn. "We can't stamp our foot and walk out again," he said. "That would be ridiculous.
"I was one of the people who voted to pull out in the first place, and I still believe that the decsion was right at the time. But we have a new ministerial team, a new work plan, and our members need us at the table."
The social partnership, which also includes the National Governors'
Association and support staff unions, has been at the forefront of reforms to teachers' pay and conditions, including reducing their workload and guaranteeing them lesson preparation and assessment time.
But this year it turns its attention to school leadership. It will provide advice to the School Teachers' Review Body about sharing leadership responsibility and accountability across a wider range of school staff, including bursars, financial managers and chief executives with no teaching experience. The NAHT, which has 28,000 members, says it represents 85 per cent of primary heads, 40 per cent of secondary heads and almost all special school heads.
Ms Keates said: "It's not the same partnership as the one they left.
There's got to be a period of time to develop trust and confidence in working togther again."