Do you know why those little white mushrooms on supermarket shelves are so tasteless? I once met a mushroom farmer who explained: "We used to take 16 weeks to grow them but with new fertilisers we can do it in a fortnight." He seemed a little ashamed for he recognised that increased "productivity" tends to conceal its costs.

Some natural processes refuse to be hurried. Growing tasty mushrooms is one. Developing a mature and informed ability to think is another.

If we design our courses so that our students are force-fed with manure, so to speak, we will be able to "produce" graduates more quickly. But will they taste of anything at all?

The point is obviously relevant when considering the overall length of degree courses. I want to apply it, however, to the length of modules, and to methods of assessment.

É«ºÐÖ±²¥

First, we need to keep one fact in mind. The time that young minds need to mature is in short supply.

The time for reading widely, for digesting new information, for exploring ideas with independence, for chatting with peers - this is disappearing fast. It is all the more important, therefore, to protect the spaces within courses.

É«ºÐÖ±²¥

Instead of which we have switched wholesale to modularisation and continuous assessment.

Short courses allow no space for developing thought, for making connections between ideas. The student is just getting the hang of the thing when it stops.

The problem is exacerbated by the unwieldy annual timetable; semesters fragmented by triennial vacations cause chaos for the development of learning.

There is a simple solution: that all courses should last a year. Immediately, overburdened undergraduates would have more time to mature.

The problem of these overburdened students has been compounded by the adoption of continuous assessment. Examinations are not foolproof; but then no system of assessment is foolproof.

Our society is dominated by the pretence that qualifications tell an exact story. It is better to recognise that all attempts to weigh achievement and potential are imprecise.

The question should not be, "How successfully do different methods of assessment assess?" but rather, "How do different methods of assessment affect our primary tasks, which are to teach and to learn?" I believe that examinations are the best way of giving freedom to both teacher and learner.

The first reason is negative. For a brief period exams dominate students' lives. But that need only happen twice in three years.

É«ºÐÖ±²¥

For the rest of the time there is freedom: freedom to take risks, because every piece of work does not count. Freedom to be ill, because a week's flu does not make a deadline impossible. Freedom to worry over a topic half-understood, or to pursue a tantalising insight. Freedom - dare I say it? - to read books that have not been prescribed.

É«ºÐÖ±²¥

To do well in an assessment you play safe and stick narrowly to the topic.

But the essence of an exam is that no one knows exactly what learning it will require. Therefore, students do not believe that comprehensive and imaginative study must be a waste of time.

The second argument for examinations is a positive one. When money and clocks were less important, a term was long enough for one topic.

Or was it? For the effect of exams was to keep alive in a student's mind all aspects of a subject until the climax of the course.

By the climax, I do not mean the exams themselves, but the period of revision. Here, more than anywhere, the student is given protected and focused time to think.

I know from recent experience. I took an undergraduate degree twice. The first time around it was the revision period that made me fall in love with the subject and continue with it after graduation.

The second time around I felt the odd moment of sheer horror - "I must be mad to do this!" But the overriding sense was one of exhilaration at grasping my subject for the first time as a detailed and interconnected whole.

Many conversations have confirmed that my experiences were not atypical.

The negative value of exams is their efficiency: they produce the required lists with the minimum disruption to the process of learning.

But their positive value is often neglected. The revision period provides a precious opportunity to mature. The more intensively we farm our students, the more precious that opportunity becomes.

Margaret Atkins is a lecturer in theology at Trinity and All Saints College, Leeds.

É«ºÐÖ±²¥