The head of a North Yorkshire primary had to make more than 60 telephone calls before she could find anyone to cover for a teacher on long-term sickness absence.
Lesley Heaton's problems were revealed after a survey of primary schools in North Yorkshire disclosed that more than 85 per cent of heads had experienced difficulties in getting supply staff.
The head of Leeming (RAF) community primary in Northallerton said: "We're given a list of supply teachers from the council, but I often get towards the end before finding someone who hasn't been hred."
Colin Culley, head of Malton community primary school, said: "I can spend hours trying to find someone to take lessons for those who are away on training, or for booster classes.
"And if you insist on supply teachers fitting in with the standards of the school, such as asking them to have marking done by the time they leave, you often find that they are unwilling to come back.
"In the end, if you can't get anybody, you either end up having to send pupils home or doubling up classes, which is clearly bad news for everyone."