A new maths teacher told a Manchester comprehensive he would only accept the job if he could work four days a week.
"A few years ago this young lad would never have dreamed of asking for a four-day week," said the head. "But they know that in this climate, they call the shots."
At a comprehensive in Ipswich, the only way the head has been able to fill his staffroom is by doubling the number of part-timers to 22. "This is the only way we have managed to fill positions," he said. "But this inevitably creates more work and means they are unable to help out with extra-curricular activities or become form tutors."
Eighteen of 65 teachers at a comprehensive in Kent are part-timers. "They tend to be middle-aged women with husbands who can support them, and who do not want to work the whole week," said the head.
"It means that you tend to have to split classes, so that pupils have, say, two teachers for maths. It's far from ideal - it is just not the same as pupils having one maths teacher."
Recruiting part-timers is often the only way schools have been able to plug gaps.
A grammar school in the East of England advertised a full-time English post three times before appointing two well-qualified part timers.
The deputy head said: "This has a major effect on the timetable. In total we now have 10 part-time staff. This not only distorts the timetable, but also removes much of the value in terms of extra-curricular activities and form tutoring, as well as making day-to-day management of departments more difficult."