The new National Association of Primary Teachers is said to have 40 potential members who believe the NAHT has hounded Chris Woodhead.
Last week the NAHT asked the Director of Public Prosecutions to prompt an inquiry into allegations surrounding sworn statements Mr Woodhead is said to have made about his relationship with Amanda Johnston, a former pupil.
Jim Hudson, leading the breakaway group, has been a long-term supporter of the chief inspector. Earlier this year, Mr Hudson, head of Two Mile Ash middle school in Milton Keynes, praised OFSTED for its professionalism and willingness to engage in a dialogue.
"I want to champion the voice of the pragmatic and reasonable primary-school teacher. The NAHT isn't doing that," he said. "We have a first-class chief inspector and inspection system. A lot of teachers who acknowledge that are not represented." His school is one of 50, identified as outstanding, involved in a school-centred teacher-training scheme inititiated by Mr Woodhead.