For many the idea of returning to a college environment to do an MBA is attraction enough. But the time spent off campus on special projects or internships may be just as important as the classroom hours - particularly if that time is spent in the workplace of a potential employer.

Huge numbers of students take an MBA in the hope of changing careers. For them the summer internship or the assessed workplace project can be the most important part of the course - because it opens new doors.

Simon Henderson, 31, is a corporate financier with Clearwater Corporate Finance in Manchester. He graduated with distinction in his 15-month International MBA at the University of Edinburgh Management School last December. "My summer internship was with Penta Capital, a private equity house in London," says Simon. "They wanted me to analyse a market and identify potential investment targets. It was a lot cheaper to get someone like me in to carry out bespoke research than instruct a firm. I recommended 10 companies which were ripe for approach, which they found useful.

"The internship helped me consolidate the skills learnt on the MBA course. As a corporate lawyer I had been advising private equity houses on the legal and commercial aspects of their portfolio but I couldn't have performed in my work placement without the MBA. It taught me how to value companies, consider market positioning of products and services. It has given me a greater holistic view of business and investment."

Three-quarters of companies which hire MBAs interview people who have done internships with them before opening the field to others, according to a survey by the Graduate Management Admission Council. Companies typically took half their MBA recruits from the previous year's internships.

"The internship is particularly important to people who are coming to the MBA to change career," says Janet Bacastow, a former investment banker who now advises London Business School students. "Firms use it as a three-month interview. It's definitely the best way into an investment bank and some of the consulting firms."

Internships can be lucrative. The traditional American course is two years. Against that the cost of the one-year programmes at some top-rated European schools looks attractive, but a summer placement can go a long way to redress the balance.

The most recent LBS class averaged earnings of £785 per week, but some students have earned about £10,000. "In the school we try to create a teamwork and collaborative environment," says Bacastow. "One thing is be a good citizen and not accumulate offers made early in the year. We have an intranet on which any firm can post a project, and those come in right up to the summer. The number of offers has increased significantly this year."

"The 12-week assessed internship can pay from between £450 a week to £1,500," confirms Clare Hudson, director of career management services at Manchester Business School. An investment bank will offer more than a start-up needing some strategic advice. "But all the companies are getting experienced people with the latest business tools and techniques."

At Manchester, she says, a few students spend as much as six months of the 18-month course out of the college: "Most students choose to do an internship. The majority of MBA hirers offer them, often to cover specific pieces of work."

Financial services firms are often on campus almost as soon as the students begin their course, from October onwards, and continue until spring. After Christmas come the blue chip telecoms, pharmaceuticals and energy companies. Smaller organisations or start-ups are more likely to recruit late, from March to April.

"Management consultancies are crying out for good people right now. They're falling over themselves to recruit," says Peter Fennah, careers director at Cranfield School of Management, which includes an eight-week assessed work placement in its 12-month course.

"Not every student wants investment banking or consulting," says Manchester Business School's Clare Hudson. "Some students are very entrepreneurial and want exposure to venture capital or private equity, and in that case the pay may not matter. The experience will be invaluable. Some companies may have a specific piece of work an MBA is ideally suited for. It could be something like helping a small start-up with their strategy."

Manchester has an incubator project backed by banks and specifically designed to help fledgling businesses develop a rigorous, sustainable business model. Many schools with 12-month courses also include such projects - often with an international flavour. But the issue of whether they are paid or not remains a grey area; and they don't usually lead to job offers.

"We have independent projects on the course but most people won't find work from them," says John Glen, Director of Cranfield's full-time MBA. "They can last from 10 to 20 weeks and often come through alumni. For example, we have recently had people working at BT on long-term customer care. But there is no official payment. The expectation is they won't get paid."

In other words, there is a big difference between a project that can be academically assessed - most are followed by a dissertation - and a summer "break" which is also a way to experience life in a completely new business environment for three months, and get paid. Such differences are often reflected in the cost of courses.

"It is one of the clear advantages of our two-year MBA," says Katie Annice Carr of IESE Business School in Madrid. "Our students have been on all sorts of placements, from the usual London investment banks to opening a micro finance facility in a poor community in Mexico."

'The EMBA marketing students' ideas offered a fresh perspective on my farm'

A disadvantage with an EMBA (Executive MBA) can be that because it is done part-time, usually by students already in employment, there is little opportunity for hands-on project work. At Newcastle University's Business School, however, there is an emphasis on practical assignments, particularly those that can help local businesses. Recently Mark Robertson, owner of the Northumberland Cheese Farm in Blagdon, threw open the doors of his business to a group of EMBA marketing students. As part of an assessed project they visited the farm, tasted the cheese, scrutinised its business operations from every angle, did some market research and offered some ideas.

"I found the marketing proposals extremely interesting and very relevant," Robertson says. "They reinforced many of my gut feelings about what we need to do as a business to grow, and they also offered a fresh perspective on how the farm could develop. I will certainly be implementing some of their ideas."