"I thought A-levels would be a doddle after GCSEs," says the son of a friend. "I couldn't have been more wrong." He is at a good school, he got a slew of As and A*s in his GCSEs in 2008, but now he is struggling.

Or, if not struggling, feeling under pressure. He will be sitting his A-levels next summer and, the way things are going, he is going to need three straight As to get into the university of his choice. What Sir Alex Ferguson calls "squeaky-bum time" is looming.

He is not alone in his anxieties. Becoming a sixth-former can be simultaneously exhilarating and scary. You have done what feels like the hard part: got your precious GCSEs in subjects you found too tedious for words. Now you have cherry-picked your best subjects, the ones you really enjoy. It should be full steam ahead to the next stations along the line – University, A Career and A Decent Salary. If only it were that simple.

"Some girls really kick on at A-level," says Marion Gibbs, headmistress of James Allen's Girls' School in Dulwich. "Others have already peaked. So many factors come into play. Children go through phases of emotional adolescence at different times in their teenage years. A-levels also demand a new intellectual approach, compared with GCSEs, which can be like jumping through hoops. You have to adopt good working habits and learn the art of independent study, researching topics for yourself."

A surprising 30 per cent of girls at the school change their A-level choices once they have their GCSE results. "Perhaps they have done better in a subject than they expected," Gibbs says. "Their confidence soars. They have discovered talents they did not realise they had. Or perhaps they have rationalised their choices and realised that taking biology, say, but no other science A-level, might not be the best long-term move."

Academically, the sixth form sorts out the sheep from the goats. That seemingly brilliant student, getting top marks at GCSE, turns out to be not so brilliant when forced to look at topics in depth, think laterally and see the connections between different areas of study. That shambling dreamer, dropping marks at GCSE through poor exam technique, becomes an intellectual powerhouse, inexhaustibly curious.

It would be nice to think that A-levels are still what they are claimed to be, an educational gold standard. Sadly, not even that can be taken as read any more.

A recent joint study by the AQA examination board and Bristol University found that, in pushier schools, a depressing number of A-level students were simply taught to cram for their exams by memorising the kind of buzz words that ticked the right boxes as far as the examiners were concerned.

Geography A-level students, for example, were coached, like trained monkeys, to include words such as ''waterfalls'' and ''potholes'' in essays about erosion. They were not given an in-depth understanding of the topic.

Hopefully, such cynicism is the exception rather than the rule. The Government is at least trying to meet concerns about dumbed-down A-level papers. Next summer, there will be tougher ''stretch and challenge'' questions, testing pupils' ability to think for themselves.

But, for students at the sharp end, that only adds another layer of pressure. Thinking for yourself can be pretty stressful, particularly when you have two dozen other things on your mind, not least what cutting-edge fashion statement to make now that you can choose your own clothes and don't have to wear school uniform.

One way or another, A-levels can be quite daunting when you get your first glimpse of the syllabus and see how much you have to raise your game after GCSEs. But a school sixth form can also be a place of rare intellectual excitement, a true spreading of wings. Above all, it is a time to be enjoyed.

LIFE AFTER GCSES

How to prepare for the next stage of your education:

Don’t slacken off your homework, just because your GCSEs are over.

Don’t lose heart if you have disappointing grades in your chosen

A-level subjects. If you are motivated to learn, you will make up the ground. You can also change your A-level choices once you have your GCSE results.

Think of sixth form as a bridge between school and university.

Read around your A-level subjects. Don’t just confine your studies to the syllabus. You are not an exam-machine any more.

Make the most of the smaller groups and take a full part in class discussions.

Give some thought to possible higher education options. 

(www.eduwo.com, Jainlyn&Charlotte)