The heads of Brooke House in Hackney and Longley Park in Sheffield joined the Sixth Form Colleges Employers Forum last month. They are the first to sign up to the sector since further education colleges were made independent of local education authorities 10 years ago.
Sue Whitham, head of the SFCEF secretariat, said: "We are delighted, considering that everyone said that our sector would be wiped out within two to three years of incorporation."
Education authorities, unions and other college leaders predicted that they would disappear in favour of further education colleges and new school sixth forms. But after an initial decline, with almost 20 closing or merging into FE colleges, they have seen a renaissance.
Research by the Learning and Skills Development Agency shows there has been a 49 per cent rise in the number of sixth-form college students since 1994, taking total numbers to 216,000.
The research, reported in FE Focus last week, also showed that the best sixth-form colleges outclassed the best independent schools while avoiding the "elitist" tag by reaching a significant proportion of under-achievers.
The two new arrivals take the number of sixth-form colleges in the learning and skills sector to 107.
Andrew Adonis, former education adviser to the Prime Minister and now head of the Downing Street Policy Unit, did little to disguise his preference for sixth-form over FE colleges. He influenced the Learning and Skills Act, which created opportunities for new sixth-form centres under LEA control but funded by the Learning and Skills Council.
Ms Whitham said: "The new colleges have signed up with us because they want all staff on our contracts, under which benefits like the Professional Standards Payments (threshold pay) are transferable to schools.
The SFCEF contract goes further than the conditions of service so far negotiated in FE colleges. Threshold payments are paid if staff pass three criteria to show effective learning in class, professional characteristics outside the class and effective teaching.
Brooke House, which opened this year, is already over-subscribed with 500 students and must therefore recruit more staff. Longley opens this autumn. It is yet to appoint a principal, and the local learning and skills council has approached the SFCEF on behalf of the governors.
The popularity of sixth-form colleges has reached such a peak in recent years that last autumn prospective students queued overnight for a place at Aquinas College in Stockport.
Ms Whitham said: "It's the sixth-form college equivalent of the first day of the Harrods sale."
Post-16 education in Sheffield; see this week's Special Report