The GCSE is the most widely held qualification by students today in the UK, mainly because it's compulsory to go to school. The General Certificate of Secondary Education is usually awarded at the age of 16 to those finishing their compulsory secondary school education. It replaces the O Level.
GCSEs and their preparation (the completion of coursework and exam revision) usually begin at Year 10 (15 years of age) but there are always child prodigies that get a GCSE in IT when they are 7 just to rub it in everyone else's faces. GCSEs can be taken in a variety of subjects, laid down by the national curriculum: English, Mathematics, Science, Modern Languages, History, Geography, Music, Art, Physical Education, and Technology. Within some subject areas, like Technology, there are various choices such as Graphics (drawing stuff), Resistant Materials (building stuff), Textiles (sewing stuff) and Home Economics (cooking stuff). Some subjects can be dropped such as Music and Art in favour of something less creative, Maths, English and Science are compulsory. The only exceptional subjects are Religious and Physical Education, who are compulsory but do not necessarily need to be taken as a GCSE. This means that non-GCSE PE is generally far more fun, going ten-pin bowling and learning Tae Kwon Do.
GCSEs are generally seen as academic qualifications. GNVQs and BTECs were introduced for those who prefer more practicality and less theory. Generally (at this level: The GNVQ is better at a higher age range) these are chosen by drop-outs who aren't allowed to leave at secondary level.
There are various exam boards (such as Edexcel) with which a school can take their exam with. Schools will therefore hunt for the easiest exam board for each subject, or the board which teaches a syllabus that the teachers think the pupils will particuarly respond to.
GCSEs aren't taken in Scotland, they have a completely different schooling system to the rest of Britain.
In the end, the GCSE is not widely considered to be a qualifaction of any worth in the big wide world, with employers favouring the new vocational qualifactions or higher level qualifactions such as A Levels and university degrees. There are some calls to abolish the qualifaction altogether and simply keep the exams to allow the teachers, and the sixth form colleges to assess student performance and only hand out certificates to those students who wish to leave the education system. This argument has gained more weight as the Curriculum 2000 A Level involves up to four examination periods within two years, which has been said to strain students unnecessarily.