The Association of School and College Leaders first sparked accusations that it was trying to expand its empire when it changed its name from the Secondary Heads Association at the start of this year.
It now intends to run a pair of courses specifically for primary heads in autumn 2006 and spring 2007, which will provide tips on inspections and staff coaching.
The ASCL's spokeswoman said the courses were a "little foray" into the primary sector and were organised at the request of primary heads. However, she stressed that the union had no intention of widening its membership beyond secondary schools and colleges. "The issues that the courses cover affect both sectors, but they are being organised by our training division and have nothing to do with our membership. We would have to change our constitution if we wanted primary heads to join."
A growing number of organisations have begun competing with unions to offer training events for senior teachers, with the National College for School Leadership, the Specialist Schools and Academies Trust and the General Teaching Council among those entering the fray in the last seven years.
ASCL membership rose last year by 7 per cent to 12,341, but it remains smaller than the National Association of Headteachers, which has members in both the primary and secondary sector.
NAHT members have been angered by the ASCL's move, but their general secretary Mick Brookes was diplomatic. He said his association already ran a comprehensive range of courses for primary heads. "We look forward to competition from the ASCL in this market and will be interested to gauge their success in making an impact," he said.