Published on December 21, 2023
Some are rehiring former teachers, according to the Association of Colleges (AoC), as an extra 60,000 students prepare to resit English and maths, many of them in two weeks' time.
Changes to grading this year meant a higher proportion of students failed.
The government says it is investing more money in colleges.
Under-18s in England have to retake GCSE English and maths if they did not get at least a grade 4 - a pass.
The resits can take place in the autumn or the summer.
Hayden, 16, has two weeks to go until he sits his maths GCSE exams again after the first time did not go to plan.
"I was hoping for a pass because I had lots of revision building up to it. When I got a 3 I wasn't too disappointed because when I did my mocks, which was just before, I got a 1," he said.
Hayden is dividing his time between his level 2 public service course and resit classes at Leeds City College. He hopes extra revision sessions over half term can get him over the line.
"Angles and ratios are probably the things I'm struggling on the most," he said.
"People should have a pass in maths because it's just that extra GCSE which can help with getting jobs in the future. It's a skill you need throughout life."
Leeds City College has had to increase class sizes in order to fit in about 600 additional students resitting English and maths this year - with some lessons growing from around 20 to 25 students.
Around a third of the students have additional needs, meaning they may need extra time in exams, or to take them in small rooms. As a result, staff rooms will be turned into makeshift exam halls for the students next month.
Once November resits are out of the way, the college will focus on preparing for what staff described as a "military operation" in the summer, when the bulk of resit students take their exams.
They will need to hire an external exam hall to fit all the students in.
GCSE passes in England, Wales and Northern Ireland fell this year - with 68.2% of all entries marked at grades 4/C and above.
The drop was steepest in England where grades were brought back in line with 2019 after spikes in top grades during the pandemic.
As a result, more than 167,000 students in England received grade 3 or lower on their maths paper this summer - about 21,000 more than in 2022.
A further 172,000 failed English language - 38,000 more.
Combined, that is the highest number in a decade.
At the same time, there are more teenagers coming through the system.
Analysis by the Institute for Fiscal Studies (IFS) suggests there will be a 17% rise in the number of 16 and 17-year-olds between 2019 and 2024 - an extra 200,000 young people.
The AoC said numbers were higher than they had anticipated, with 88 out of 98 colleges that responded to a survey seeing an increase in resit numbers over the past year.
The membership body, which represents 215 out of about 225 colleges in England, said a lack of English and maths teachers meant the compulsory resit policy was not "sustainable".
Catherine Sezen, director of education policy at the AoC, said: "Some colleges are having to rehire retired teachers, employ agency staff, rely on non-specialist staff to teach lessons and share staff with other colleges.
"The decades of underfunding and under resourcing means that, despite recent funding boosts from the government, college finances are still under extreme pressure and some do not have the funding or staffing levels to cope with the increased numbers of students needing to resit."
The pass rates for resits is low. This summer, 16.4% of people aged 17 and over taking their maths GCSE resit passed, compared with 25.9% of those taking English.
The policy was introduced in 2014, making it compulsory for under-18s without a pass in GCSE English or maths to continue studying that subject.
These students are more likely to be from a disadvantaged backgrounds and the vast majority enrol on courses in further education colleges rather than school sixth forms or sixth form colleges.
Some of them end up resitting multiple times.
A spokeswoman for the Department for Education (DfE) said: "Young people who leave education with a good grasp of English and maths have a much better chance of securing a job or going on to further study."
The DfE said it was investing an extra £1.6bn in colleges by 2024-25, compared with the 2021-22 financial year, and an extra £470m over the next two years would help colleges boost recruitment and retention of staff.
The IFS said that money would "just about allow [colleges] to match this year's pay offer of 6.5% for teachers".
This month, the government also announced a further £150m per year over the next two years to help colleges with students taking resits and laid out plans for the Advanced British Standard - a new qualification that would include some English and maths to 18.
Prime Minister Rishi Sunak said more teachers would be recruited to help.
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