Emma Stainer, 18, an A-level student at Wallington High School, gave up the retail job she found during her lower sixth year because her studies were suffering.
She was contracted for 12 hours, but found herself working longer because of stock-taking and training sessions.
She now works similar hours at a nearby golf club, which is happy for her to take school books into work to read during quiet spells.
"My results were not what I wanted. They have now gone up from D to A grades," she said.
"I have to buy books for school and buy my clothes. You have to do more hours than you want to because of it.
"The main supermarkets say if you work the hours they want, when you move to university they will find a place in their store near the university you have gone to.
"I don't think there are enough incentives to stay on at school after 16. You can stay on, run up debts, go to university and pay tuition fees - or go straight into a job and progress that way. There is no way I wouldn't go to school and university, but there are some people who have left at 16 and are in managerial positions."
James Baker gave up his commission-based double-glazing job because of parental and school pressure. The 18-year-old, studying four A-levels at Wilson's School, Wallington, was earning Pounds 15 an hour and using a mobile phone in school breaks to arrange customer appointments. He was working all weekend and some weekdays. His grades have improved significantly since he gave up the job.
"The money was good but I gave it up because of pressure from my parents and the school," he said.
"But when I went for university interviews, they said they were impressed with my work experience."