More headteacher jobs were advertised in The TES last month than at almost any time in the past seven years.
There were 455 posts advertised for the first time in January 2004, a rise of almost a quarter on the average for that time of year.
Professor John Howson, director of Education Data Surveys, said: "We are now starting to hit what everybody knows is coming.
"There is an increase in the numbers of people reaching retirement age and this is compounded for heads by two things: the need to introduce the workload agreement and anxiety about funding.
"If you are coming up to retirement age and have problems relocating more than 20 administrative tasks and with general budget chaos you might think it is more sensible to go now and spare yourself the aggro."
The advertisements were in search of 356 primary heads, 76 secondary heads and 23 special school heads - with most posts due to become vacant at the end of the academic year.
Geoff Handley, 56, who has been head at 215-pupil Fishburn primary, near Stockton-on-Tees, for the past 14 years, is taking early retirement this summer.
He said: "When I first took over as a head, it was a time of great change with the introduction of local management of schools and the national curriculum.
"I found that quite exciting. I probably spent the first 10 years of headship very motivated, but the past two years have been a lot more challenging.
"The difficulties with funding have hit me very hard. There seems to have been a lot of change for change's sake and I think I'm vocationed out."
Peter Helyer, head at 125-pupil Bemerton St John Church of England primary in Salisbury, will be 60 when he retires.
He said: "There is an awful lot of pressure from the league tables. I don't feel I have to leave, but I have seen people go on beyond 60 and that's when it really does become too difficult.
"I am seen as old. I know a couple of heads who left at 55 because it got too much."
Last month's surge in headship advertisements was the third biggest in recent years. The record of 553 vacancies was set in January 1997 when there was a sharp increase in resignations owing to the change in the early retirement rules. The other peak month was March 2001 when 469 posts were advertised.
David Hart, general secretary of the National Association of Head Teachers, said: "Heads are facing a lot of challenges. The funding crisis certainly won't have helped, there are the demands associated with the workload agreement, the performance-related pay system and the changes to the Office for Standards in Education framework.
"There is no doubt that, unless we solve some of these issues, the situation will grow worse. These figures represent a challenge for the Government. We can ill afford to lose so many heads at the present time."
The figures come after a report last term found schools are still struggling to find new heads and deputies, with half of primaries receiving five or fewer applications for the top job.
Professor Howson said: "If there is any reluctance by deputies to take on jobs then we will have a significant issue, particularly in primary schools."