They are the staff who, according to Paul Hammond of the National College for School Leadership, can "give the head confidence that the implementation of new initiatives is being looked after by the middle tier, freeing senior management up for strategic thinking".
Mindful of this, the college will, in September, introduce Leading from the Middle, a three-term professional development programme aimed at teams of subject leaders. The aim, says Mr Hammond, is to do something different from the standard one-off training session.
"The traditional approach," he says, "is a one day course with a good speaker and a PowerPoint presentation. Everyone goes home and not much happens. We are trying to align our programme to be the antidote to that."
With this in mind, participants are allowed to enrol not as individuals but as teams ("learning sets") of two to four subject leaders plus a senior colleague who will act as "coach" to the team. College support comes from a tutor - a serving head or deputy or one of the college's consultant leaders. There are some face-to-face sessions, and web support, but the real learning happens in school, working on genuine innovation and development that's in line with the school's own vision.
As you'd expect, given where it comes from, the emphasis is on leadership rather than on specific management skills. So, for example, Nicola McLeod, appointed head of modern languages at the 1,300-pupil Priestnall school in Stockport a year ago, says: "It's more about taking things forward - how to manage change and less about how to move paper."
A fairly new head of department, she aims to build teacher and student motivation in a subject that's often relatively unpopular. In the process she is learning about handling people. She has become more confident about conducting meetings, is ready to accept alternative opinions and to judge when to accommodate them, and when to move on decisively.
"I plan meetings now and have a clear purpose to them. I'm not afraid to ask for different points of view, and people are not afraid to put across their ideas."
Hers is a story of increased confidence that allows her to know when and how to accept alternative suggestions. This, in turn, enhances the professionalism of colleagues; motivating them and making them feel valued.
Her experience, in fact, brings to life Paul Hammond's idea that the programme is about, "making sure that leaders do have vision and values, drive and direction, but know how to take people with them".
Nicola McLeod is relatively new to middle management, but Paul Hammond is at pains to emphasise that "Leading from the Middle" demonstrates the college's commitment to leadership right across the profession.
"There's been this assumption that we've only been there for secondary heads," he says, "but here we have a programme that can apply, for example, to a primary geography co-ordinator who's been teaching for only a couple of years."
'Leading from the Middle' will be available nationally from September.
Online applications opened on May 21 and run to mid-June. There will be 2,000 places in the first cohort. See the NCSL website: www.ncsl.org.uk