Some jobs in teaching seem impossible. There's special educational needs co-ordinator, for example (all children have needs, all needs are special - and there's class teaching to do as well), and head of music (teach the subject, put on concerts, dignify speech day, keep the instrument teachers happy, find the missing bassoon, get the orchestra into the school proms).
Somewhere high on this list must lie the post of deputy head of a primary school. Jill Hallsworth, enthusiastic deputy of the 450-pupil Lydgate junior school in Sheffield, explains: "The job combines being an expert in the classroom - a role model for colleagues - with significant management responsibilities."
Almost all primary deputies have a teaching load, often with only a small amount of non-contact time for management work. In effect, they are doing two full-time jobs.
Much of the work is done outside classroom hours - all teachers routinely hold planning meetings and attend courses in twilight time, and governors'
meetings are invariably evening affairs. But it seems neither fair nor feasible for a primary deputy to do the job without some non-contact time during the day - observing and supporting colleagues as they teach is just one of the management tasks that can be done only by visiting working classrooms. How much time the deputy spends out of class varies significantly from school to school. Surveys carried out by primary deputies in Sheffield reveal wide differences - from a few hours a week to several days. The size of the school makes a difference, but that's not the whole story.
Budgets vary, for instance, so a school that has extra funding for beacon status or from an action zone will have correspondingly more flexibility in the way it uses staff. And, in many authorities, junior schools with only key stage 2 pupils fare relatively badly against all-through primaries because funding is skewed towards key stage 1.
It isn't only about funding, though. Priorities come into it, too. For example, primary heads have traditionally signalled their commitment to the principle of non-contact time by taking the deputy's class for some sessions. Mary Shipley, head of Hunter's Bar infants' school in Sheffield, says: "When I became a deputy that's how I got my non-contact time." But it doesn't solve the problem of creating time for head and deputy to meet. "It makes forging a relationship difficult," she says. "You need the quality time together to drive things forward, share responsibilities and gain the professional development that helps a deputy make the next step into headship."
For Mrs Shipley, who was active in Sheffield's primary deputies' group before becoming a head, it's not just a matter of will, but also of money.
"It's about budget priorities," she says. The implication is that heads and governors have to employ enough staff to give the deputy free time. The job of headship is becoming too big for one person. "The key processes of leadership and management are radically different now from what they were 10 years ago," says Mrs Shipley. "Yet in many cases, the expectation in a primary school is that one person will continue to do it all. It doesn't take much to see that this will produce an excessive workload."
Part of the answer, perhaps, lies in trying "flatter" kinds of management structure, with greater equality of partnership between heads and deputies.
That's one of the areas being studied by the Sheffield deputies' group. The existence of this supportive band of people, all of whom understand the pressures, and who are finding ways of dealing with them, is important for morale. "Networking is part of what makes the job enjoyable," says Ms Hallsworth.
The group addresses a plethora of problems and issues. Pay is one, because in some circumstances the differential between the salaries of teachers and deputy heads isn't attractive. Then there's increasingly clear evidence that many deputies - about half of those in Sheffield, according to the deputies' group - don't want to be heads. "There's a huge issue for recruitment," says Ms Hallsworth, "if half of our primary heads are not going to come from the ranks of the deputies."
Despite the talk of pressure, survival and overload, she is at pains to emphasise that she's far from negative about the job. "We do thrive on it," she says. "It's the demanding and varied nature of the job that makes it so good."