The youngest children start their education in a crèche /kreʃ/, where they mostly play but also do some early learning activities. After that, they may go to a nursery school. Between the ages of five and 11, children attend primary school, where they learn the basics of reading, writing, arithmetic, etc. For most children, secondary education begins when they enter a comprehensive school or a more traditional grammar school (to which they gain admission by sitting an exam). The famous UK public schools are in fact private, fee-paying schools. Between the ages of 11 and 18, young people take a wide range of subjects in arts, sciences and technical areas. In the UK, pupils can leaves school at the age of 16, although many young people choose to remain in full-time education until the age of 18. (In England it is compulsory for young people to continue with some form of education or training until they are 18 [they must do it], even if they also have a job.) From 16 to 18 young people may study at secondary schoolor at a sixth-form college, after which they may go on to higher education.

You take/do/sit an exam or resit¹ an exam. At schools and sixth-form colleges in the UK, students have to take formal end-of-year exams. At 18, a lot of students sit their university entrance exams, commonly referred to as ‘A levels’ . Students are usually given marks (e.g. 75%) or grades (e.g. A, B+, C).  If you pass and do well, you get a high grade; if you fail, you don't get the minimum grade. If you skip classes², you'll probably do badly in the exam.