To ensure both breadth and depth of knowledge and understanding, students choose courses from the following subject groups: studies in language and literature; language acquisition; individuals and societies; sciences; mathematics; and the arts. Most subjects may be taken at either standard level (SL) or higher level (HL).
SL courses ensure students are exposed to a range of disciplines that they might otherwise opt out of, and HL courses allow students to spend more time with subjects they are more interested in by exploring options in addition to the SL core curriculum. In this sense, all DP courses, regardless of whether they are SL or HL, are integral to the programme.
Both SL and HL courses are meant to span the two years of the DP. SL courses are recommended to have at least 150 hours of instructional time, and HL courses are recommended to have at least 240 instructional hours.
In most cases both SL and HL courses consist of the same educational aims, core syllabus and curriculum and assessment models. HL courses typically also include a range of additional elements designed to allow students to explore areas of interest within the subject in more depth. In this sense, SL courses are not watered down versions of their HL counterparts. The assessment criteria are equally demanding for both levels, and SL exams are marked and standardized with the same rigor as all IB coursework.
Source: Standard level and higher level courses