Ages 5-11: Primary School. This is split into two Key Stages, Key Stage 1 (5-7) and Key Stage 2 (8-11). At the end of each, children take SAT tests, which aren't particularly important, but are a decent monitor of progress during the child's early years.

Ages 12-16: Secondary School. Again, this is split into Key Stage 3 (12-14) and Key Stage 4 (15-16). At the end of KS3, there are more unimportant SATs, but at the end of KS4, we take GCSE's. These cover a broad range of subjects (English, Maths etc. are compulsory, others are selected by the students themselves) and are the first important exams that a child will take. After that, they can either leave school and get a job, or move on to the Sixth Form/College.

Ages 17-18: Sixth Form/College. In the first year, we take 4 'AS-levels'. Then we drop one subject and do the all-important 'A-Levels' in the second year. At this stage, no subject is compulsory, so students are free to select whatever they wish, and can begin to specialize in certain fields. Afterwards, a student can either leave school or continue on to University.

18+: University. Here, students study a single subject. The length of the course will depend on the subject being studied. At the end of this, the student will emerge with a Degree. They can then go on to study other subjects if they wish, but only crzay people do that.

In summary:

Primary School, Ages 5-11. SAT tests
Secondary School, Ages 12-16. SAT tests and GCSE's
Sixth Form/College, Ages 17-18. AS-Levels and A-Levels
University, 18+, Degree.

There's also all sorts of other qualifications, such as GNVQ's, but they're not really a part of the school system, so I've left those out.