When Nilesh Limani opened his A-level results a year ago he was not “shocked” – because he had realised even when he was sitting the exams that he was not at his peak – but he was still “disappointed”.

Nilesh, now 19, had notched up a B in psychology and two Cs in biology and chemistry. Last summer’s worse-than-expected results seemed to have dashed his hopes of becoming a dentist and he was faced that morning with a difficult decision: should he enter clearing and look for a place on a pharmacy degree course, his fall-back career choice, or go back to school and resit his A-levels.

Back home in north London Nilesh’s cousins turned up to give advice. Some of his relatives had retaken their A-levels and Nilesh decided to follow the same path.

“You have to hold out for something you want to do. It is your career at the end of the day,” he says. His gamble paid off. Last Thursday Nilesh was cock-a-hoop after gaining the three A grades he needed to enrol on a dentistry degree at Queen Mary College.

Resits are the most logical option for a student who has considered clearing places and decided instead to pursue a particular degree. Nilesh enrolled at Brampton college, one of the biggest fee-paying sixth form colleges in London, where weekly tests ensure that students stay abreast of their study.

Private A-level tuition does not come cheap. The cost for retaking all six modules in one A-level at Brampton in January after five months’ study is £3,285. Retaking in June after a year’s study costs £5,835. Most students resit one, two or three modules in their weakest subjects.

Bernard Canetti, Brampton’s principal, says around 45 of the college’s 250 students are “resitters”. “It’s usually a question of motivation,” he says. The college interviews students to make sure that they are “committed to the course they want to do and will put in the work”.

But if they are accepted, continues Canetti, most resit students perform better second time round. “We have a lot of people who come in with C grades and go out with As.

“If you are retaking all three A-levels over the year [at a cost of around £15,000] it is a lot of money,” admits Canetti. But, over the course of a lifetime’s earnings in a highly paid profession such as medicine or dentistry, he points out, many parents feel that the cost will be recouped.

At Brampton, Nilesh started biology A-level from scratch, with a different exam board, and also retook some of the six modules that made up each of his A-levels in psychology and chemistry in a bid to boost his grades. “I still remember how I was feeling on results day last year,” says Nilesh. “I was fed up I had to retake and rerevise. But the year went unbelievably fast.”

His message to other teenagers who have missed out on the grades they need for their chosen degree course? “Do not despair. Think about what you want to do in life and make your decisions according to that. I would definitely recommend retaking. I thought everyone would be a year younger than me at the college but at least 25 were in the same situation.”

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