So what makes a teacher like Steve give up several weeks of his vacation for more time in the classroom? "A bit of extra cash", as he says, is the most obvious answer. This is a summer revision course for GCSE, A-level and international baccalaureate students run by Oxford Science Studies, where teachers can earn up to pound;1,000 a week for intensive tutoring.
But for Steve, who has taught physics for 12 years at the Royal Hospital School, Ipswich, there are other benefits, too.
"I enjoy the atmosphere," he says. "It's very relaxed and the other members of staff are interesting people. You don't get to know the students as well as you do in school, but the teaching is much more focused because you're concentrating on the essential parts of the subject.
"It's also more varied, because you're dealing with different syllabuses. Topics can come up that you haven't looked at for years and that's quite stimulating."
Oxford Science Studies was set up in 1997 by Dr Mario Peters, then a research physicist at Oxford University who had developed a liking for teaching and wanted to establish revision courses that adopted the Oxbridge tutorial approach. His first tutors were science PhDs from the university who were embarking on PGCEs. As demand for the courses grew, he began to advertise for teachers, too, in a wider range of subjects.
"It turns out that teachers, like academics, value the chance to earn a bit more in the summer," says Dr Peters.
Summer courses took longer to catch on with students compared with the more popular Christmas and Easter courses that Oxford Science Studies also runs. Dr Peters' first summer course, for which he hired a whole college, attracted only three boys. But numbers have grown to 70 students a week in the summer, including some from overseas. The residential courses are held in the traditional public school environment of St Edward's, Oxford, and the average class size is two to three, with many students taught on a one-to-one basis.
"From the teachers' point of view, the summer course is probably the nicest one to teach," says Nick Strugnell, course director. "The students aren't freaking out about their exams and there is time to address any problems calmly."
Nicola Marshall, a biology teacher from Tudor Hall School, near Banbury, has been teaching on the courses since she finished her PGCE eight years ago (see box, above). She is glad of the extra money but also likes the fact that the summer courses set her up really well for the autumn in terms of sharpening her subject knowledge.
Renata Calverley taught English for 35 years, including 20 years at Aylesbury High School, Buckinghamshire, and has been involved with Oxford Science Studies since she retired seven years ago. "I genuinely love teaching and that is why I started tutoring when I retired. I find these courses very worthwhile and I think we do help a lot of people in all sorts of ways." She works with the pupils one-to-one and finds them "very interesting". In tutoring, she says, "you can focus in and help someone with their particular needs. I don't see myself as a great academic, but I think I can enthuse people because I love the subject and I believe in what I'm doing."
Today she is looking at passages from Ernest Hemingway's In Another Country with 17-year-old Norwegian student Mildred-Marie Dargvik, who is finding the book and its war subject matter difficult. They take it in turns to read passages aloud, analysing meaning and nuance, and Renata broadens the discussion to include First World War poets.
Mildred-Marie, who speaks English fluently, has come to Oxford Science Studies to brush up on her chemistry, maths and biology, as well as her English, for her International Baccalaureate next summer. "It's very useful because you can tell the tutor what you want to do so you really understand the topic rather than rushing to get through the syllabus as we do at school," she says.
Some students come to catch up on topics they've missed or struggled with, others come because they want to make sure of getting top grades. Some are there unwillingly because their parents have insisted on it. But the tutors say even students who start the week looking grumpy usually end up getting something out of it some even signing up for an extra week of their own accord.
"My mum made me come and I wasn't very pleased," admits Lara Dunlop, 15, from Somerset. "But it's been good. I understand things properly now because it's only three in a class and you get more attention. I think I'll know a bit more when I start school again in the autumn."
Zoe Gracey, 15, attends Tonbridge Grammar School in Kent.
"It was my mum's idea for me to come. She thought I should catch up on stuff because I hadn't done that well last year. I wasn't too happy to start off with because this is the holidays.
"I'm here for two weeks and I'm doing GCSE maths, three sciences and IT. They are quite weak subjects and I want to be a vet when I'm older. This is my second day and so far I've had biology. In the first lesson, I didn't know that much but after the teacher explained it, it was OK.
"It's quite different from school more one-to-one and more hands-on. If someone doesn't understand something, the teacher goes through and explains it more slowly. At school there's 30 in a class and I can't concentrate that well because there's a lot of talking. You can concentrate more here.
"You have a lesson and then you have a study period, when they give you sheets to go and do by yourself. You finish at 5.40 and then there are evening activities. Most people are friendly. I'm actually enjoying it and yes, I'm a bit surprised."
Nicola Marshall (pictured) is a biology teacher from Tudor Hall School, near Banbury.
"I started teaching for Oxford Science Studies in 1998, the year after they set up. Partly it's useful to have a bit of extra money so you can treat yourself to a nice holiday, or do something to your house. This year, for example, the extra cash will pay for a new fireplace, which I wouldn't have been able to afford otherwise.
"But the other really good thing about these courses is that my subject knowledge improves, so that when I go back to school in September, I feel on top of things. Otherwise, your brain can go a bit numb over the summer. I want my students at Tudor Hall to do really well and if I can go back with more ideas about how to structure lessons and where the misconceptions are, I'll be doing them a better service.
"I absolutely love the teaching here. I'm not teaching topics from scratch and I like the quick pace, the quick-fire questions and the opportunities to relate topics to things in the news. I also like the other tutors. People with different interests and specialisms can be quite inspiring and it stops you getting stale."