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The General Certificate of Secondary Education (GCSE) is an academically rigorous, internationally recognised qualification (by Commonwealth countries with education systems similar or identical to the UK education system) awarded in a specified subject, generally taken in a number of subjects by pupils in secondary education in England and Wales over two years (three years in certain schools). It was introduced in the UK in 1988 to replace O-level and CSE examinations.

One of the main changes to previous educational qualifications in the United Kingdom was to allow pupils to complete coursework during their two years of study, which was marked by their teachers and contributed to their final examination grade. There has been a move recently from doing coursework and modular examinations for part of the course when pupils would take exams throughout the course to an end of year exam after the two years of study (a 'linear' series). The exams are being revised to make them more difficult such as testing skills from a whole text in English instead of part of a text. Coursework has now been replaced by Controlled Assessments in certain subjects, in which the student completes a number of assessed pieces of work which will ultimately count towards their final examination grade in the specified subject. The Controlled Assessment component of the qualification is usually done under exam-style conditions. After major GCSE reforms, coursework/controlled assessment generally have little to no influence on the final grade as opposed to the past.

The qualification is equivalent to a Level 1 or Level 2 (grade depending) Key Skills Qualification (in Scotland, the equivalent is a National 5). Some pupils may decide to take one or more GCSEs before or after they sit the others, and people may apply to take GCSEs at any point either internally through an institution or externally. A level 1 GCSE covers grades C to G or 1 to 5 (commonly referred to as the foundation tier) whereas a level 2 GCSE covers grades A* to C or 4 to 9 (commonly referred by as the higher tier). Five level 2 GCSEs, including English and Maths, are generally required (as well as an A or B in the specific subject) to continue to the level 3 Advanced GCE level (A-Level) or equivalent level 3 qualifications. From September 2017, grades will be awarded from 9 to 1; a grade 9 being equivalent to an A** and a grade 1 being marginally better than a U (unclassified in the former system). Some schools start GCSEs in year 9.

The education systems of current and former British territories, such as Gibraltar,^[1] and Nigeria, also offer the qualification, as supplied by the same examination boards. Other former British colonies, such as Singapore and Zimbabwe, continue to use the O-level qualification.^[2] The international version of the GCSE is the IGCSE, which can be taken anywhere in the world, and which includes additional options relating to coursework and the language the qualification is pursued in. All subjects completed in the fifth of the European Baccalaureate are generally equivalent to the GCSEs subjects.

Prior education to GCSE level is generally required of pupils wishing to pursue A Level courses or the BTEC Extended Diploma and International Baccalaureate. GCSE exams were introduced as the compulsory school-leavers' examinations by the government of the United Kingdom. GCSE examinations are typically taken at the age of 16 but may be taken at any age.

BTECs can also be taken. These are marked with a different grading system: level one, grades D-G, and level two, pass (C), merit (B), distinction (A), and distinction* (A*) (Pronounced distinction-star) New regulations require that BTECs now include some form of examination, usually done online. The difference between BTECs and GCSEs is that the BTEC course is heavily coursework-based.

At the end of the two-year GCSE course, on the third Thursday of the August of that year, candidates receive a grade for each subject that they have sat. Before the transformation of the GCSE grading system from alphabetical to numeric grades, the pass grades, from highest to lowest, were: A* (pronounced "A-star"), A, B, C, D, E, F and G. Grade U (ungraded/unclassified) signifies that a pupil achieved nothing worthy of credit, therefore no GCSE is awarded to the pupil in that subject. For GCSEs after reformations, the pass grades are: 9, 8, 7, 6, 5, 4, 3, 2 and 1 but a 'good pass' which is generally required, is grade 4 or higher. The U grade stays the same as mentioned above.

Broadly, the same proportion of students will achieve 4 and above as currently achieve C and above, and the same proportion of students will achieve grade 7 and above as currently achieve A or A* ^[3]

GCSEs are part of the National Qualifications Framework. A GCSE at grades D to G (or grades 3 to 1) is a Level 1 qualification, while a GCSE at grades A* to C (grades 9 to 4) is a Level 2 qualification. GCSEs at A* to C or 9 to 4 (Level 2) are much more desirable and insisted on by many employers and educational institutions. Level 2 qualifications are usually required to advance to Level 3 qualifications.

Pupils can also receive an X grade which signifies that they have completed only part of the course or that key elements such as coursework are missing and so an appropriate grade cannot be given. A Q (query) grade means that the clarification is needed by the exam board, whom the school should contact. Both X and Q are normally temporary grades and replaced with a regular grade (A* to G or 9 to U) when the situation has been resolved.

X grades are also very rarely used by some exam boards to indicate that the examiner found offending material, usually hate speech, within one of the exam papers that a pupil took. In some cases this may cause the pupil to lose all marks for that particular paper, and occasionally for the entire course. X grades are most common in subjects where ethical issues are raised and/or there is a question which requires the pupil to express his/her personal opinion on a scientific/religious view. Notable areas where this can occur are Biology and Religious Education/Studies.

After GCSE reformations, the grading system changed as follows: instead of grades ranging from A* to U, they now range from 9 to 1 with 9 being the highest grade achievable. This has been introduced because exams are seen as becoming easier each year with a larger number of pupils achieving A*. Changing the grading system also allows the exam boards to increase the difficulty of the exams and therefore have fewer pupils who achieve the highest grade, and get a more accurate representation of the pupils' capabilities. It also gives the exam boards a chance to add extra grades on if the exams start becoming too easy again, which is not possible with the A* to U system. English and Maths exams are being trialled using the new grading system in the 2015/2016 academic year.