Government efforts to help schools keep hold of teachers and develop their skills do not appear to be working, the government spending watchdog suggests.
A National Audit Office report shows more teachers leave before retirement than five years ago, and schools are finding it tougher to fill posts.
In 2016, nearly 35,000 teachers – 8% of the workforce – left their jobs for reasons other than retirement, it said.
The government said it was tackling the challenges facing schools.
The NAO said that between 2010 and 2016 the number of teachers in England’s state schools increased by 15,500.
But over the same period, the number of secondary school teachers fell by 10,800.
Secondary schools are now facing challenges to keep pace with rising pupil numbers, it said.
A Department for Education survey quoted in the report found teachers and middle-leaders were working a 54-hour week.
Schools are only filling half of vacancies with teachers having the required experience and expertise, it said.
It also found local variations in the proportion of schools reporting vacancies.
The North East had the lowest percentage of schools (16.4%) reporting at least one vacancy, while the South East had the highest at 26.45%.
The NAO report is the latest in a long line of reports to highlight the problems schools have with recruiting.
A greater number of qualified teachers are returning to state-funded schools, the report found – with 14,200 teachers returning in 2016 – an increase of 1,110 on 2011.
The report also found the DfE had not set out in a coherent way, or shared with schools and teachers, how they can work together to improve things for the workforce.
The NAO said it previously reported the DfE spent £555m on training and supporting new teachers in 2013-14.
In contrast, £35.7m was spent in 2016-17 on programmes for teacher development and retention, with £91,000 of this aimed at improving teacher retention.
Head of the National Audit Office Amyas Morse said: “Schools are facing real challenges in retaining and developing their teachers, with growing pupil numbers and tighter budgets.
“The trends over time and variation between schools are concerning, and there is a risk that the pressure on teachers will grow.
“Since having enough high-quality teachers is essential to the effective operation of the school system, these are issues that the Department for Education needs to address urgently.”
A Department for Education spokesman said: “We continue to invest significant sums in teacher recruitment with £1.3bn up to 2020 being invested in teacher bursaries to attract the best and brightest into the profession.
“We recognise there are challenges facing schools and we are taking significant steps to address them.
“We have established a £75m fund to support high-quality professional development in those schools where teacher retention is an issue, and we are making it easier to advertise vacancies.
“In addition, we are working with Ofsted to tackle workload and will continue to engage with the profession to better understand the specific challenges and how we can address them.”
Chairman of the Public Accounts Committee Meg Hillier said workloads were one of the main reasons teachers leave the profession, yet the DfE expects schools to make efficiency savings in staffing – which means fewer teachers.