The 56-year-old leaves his post as head of a small, successful junior school in Nottinghamshire today to become general secretary of the country's biggest heads' union.
His departure from Sherwood junior has brought into sharp focus one of the challenges he will face as leader of the National Association of Head Teachers. The school, which has almost no truancy and recorded better key stage 2 test scores than the national average last year, received just three applications when the headship was advertised last month.
Mr Brookes, who takes over from David Hart, the long-running NAHT leader, in September, said: "This is a very successful school where people like to work and often stay for a long time.
"If a school like this cannot attract a large number of candidates, then I think some very serious questions need to be asked."
Mr Brookes said the workforce agreement, which aims to give teachers at least half a day a week outside the classroom for planning and marking from September, had placed massive pressures on heads. The NAHT has already pulled out of talks surrounding the agreement amid rows over a lack of cash.
"Part of my warm-up to the job as general secretary has been to travel around the country listening to headteachers," Mr Brookes said. "One of the strongest messages I am getting is that heads are doing all they can to better the working conditions of staff but are taking on much more work themselves in the meantime.
"Unless this issue is addressed soon, we are going to be in an awful lot of trouble."
Sherwood junior, which is offering a salary of up to pound;50,000, has advertised Mr Brookes' job twice in the past two months and received only three applications each time, fewer than most other schools.
Although governors have now picked out Mr Brookes's successor, the new head cannot start until January, leaving a deputy in temporary charge.
This year the average, mid-sized primary received just six applications for a vacant headship, junior schools saw five and infants four.
John Howson, a recruitment analyst, said the number of schools looking for a new head was likely to reach 2,500 this year, only slightly less than the 2,688 vacancies advertised in 2004.