Students taking the International Baccalaureate have to study subjects from six groups, including maths, literature, science and a foreign language.  Three subjects are taken at Standard Level (SL) and three at Higher Level (HL).   There are two exam sessions a year - in November for the southern hemisphere and May for the northern hemisphere.  The IB is a linear exam taken at the end of two years of study, and individual exams cannot be retaken.