Private tuition takes many forms, from the professional colleges which advertise in newspapers to individual teachers who find pupils by word of mouth or through signs in shop windows.
Basil Paterson Tutorial College in Edinburgh's New Town was founded in 1929 and has been delivering Easter revision courses since the late 1960s. With many individual schools, both local authority and private, now running their own Easter revision schools, numbers are down this year by nearly a third.
"This year we have about 70 students taking classes or individual private tuition, compared to about 100 last year. It's the classes that are down rather than the one-to-one tuition," says college principal Iris Shewan.
"We're being pushed towards our core business, the normal classes and tutoring we offer throughout the year," she says.
Last year the college ran two English Higher classes - each with a maximum of eight pupils - compared to only one this year.
"It tends to be the core subjects that attract pupils. This year the busiest classes are maths and the sciences - physics, biology and chemistry. Normally English would be up there too."
The two weeks of Easter courses offer two hours of tuition per subject per day plus homework. The first week mostly attracts pupils from private schools, which break earlier; the second week sees a mixture of local authority and private students. The norm is for pupils to take two subjects.
There are no classes for Standard grade subjects, only private tuition.
"When students enrol we send out a checklist to find out their weak areas so that the tutor can address them. It also means the students will have done some self-analysis before they start," says Mrs Shewan.
"With a maximum of eight per class, it means pupils remain individuals and their weak points can be addressed.
"Covering the main points, every course is a balance between theory and examples. The fact that it is specifically structured gives students confidence because they know their revision is being properly targetted."
Most of the tutors are college staff, though an extra four are drafted in from both local authority and private schools.
All the tutors are registered with the General Teaching Council, says Mrs Shewan, bar one who has taught in a private school, and the tutors range in age from late 20s to near retirement age.
"It's pretty much a policy thing. Retired folk can have out-of-date ideas or might not be up to date with developments such as Hiher Still. If you're selling something like this, it's got to be right," she says.
"Some schools are happy to recommend us, but more so the private ones as their parents are more accustomed to paying.
"Some local authority schools are not keen on topping up because they see it as an unfair advantage for those who can afford it. However, we're not talking about pound;17,000 per annum fees here. We're talking about pound;100 for a week, which the majority of parents could afford.
"Each parent will do the best for their children. Some choose to top up this way.
"I don't think it's about an unfair advantage. If you're brought up in a house with a lot of books and you're encouraged to read as a child, you already have an educational advantage over a child who isn't.
"I'm not saying that compares exactly with private tuition. What I am saying is that in education there isn't a level playing field to begin with."
Mrs Shewan argues that the college does not run in competition to local authority Easter revision courses. "I think we're more complementary than competitive, and I'm all for them, especially for parents who couldn't afford to send their kids here."
Sandra Simpson, the City of Edinburgh's development officer for study support, would make no comment on private institutions such as Basil Paterson college.
"The City of Edinburgh is delighted we have a very strong revision programme in our schools and are confident that our pupils will have every opportunity to receive the support they may need within the provision our schools are making," she says.
Basil Paterson college draws its Easter revision pupils not only from local authority areas such as Edinburgh, the Borders and Fife, but also from private schools ranging from the south of England to the Highlands of Scotland.
"Parents just realise it can be very difficult to focus over an Easter break, especially in private schools which can break for up to four weeks at this time of year," says Mrs Shewan.
"It gives the students a timetable, stops them sleeping in till 11am and then spending the rest of the day on the phone to their friends."
Small class sizes are an attraction, as is the provision for one-to-one tuition.
"The one-to-one students are not necessarily the weaker ones. It can be more to do with grades."
This is also the case generally.
"In the Seventies and Eighties the aim of the students was more to get a pass. Now they come to get A or B grades.
"I think this is partly because universities are looking for better grades and parents are more aware of the pressures to get into university.
"It's often the weakest subject they come for but sometimes it's to ensure a really good grade."