(age 13–14), as well as the mathematics to be learned in high school. The standards do not dictate any particular pedagogy or what order topics should be taught within a particular grade level. Mathematical content is organized in a number of domains. At each grade level there are several standards for each domain, organized into clusters of related standards. (See examples below.) In addition to detailed standards (of which there are 21 to 28 for each grade from kindergarten to eighth grade), the standards present an overview of "critical areas" for each grade. There are six conceptual categories of content to be covered at the high school level: Number, and quantity; Algebra; Functions; Modeling; Geometry; Statistics and probability. Some topics in each category are indicated only for students intending to take more advanced, optional courses such as calculus, advanced statistics, or discrete mathematics. Even if the traditional sequence is adopted, functions and modeling are to be integrated across the curriculum, not taught as separate courses. Mathematical Modeling is a Standard for Mathematical Practice (see above), and is meant to be integrated across the entire curriculum beginning in kindergarten. The modeling category does not have its own standards; instead, high school standards in other categories which are intended to be considered part of the modeling category are indicated in the standards with a star symbol. Each of the six high school categories includes a number of domains. For example, the "number and quantity" category contains four domains: the real number system; quantities; the complex number system; and vector and matrix quantities. The "vector and matrix quantities" domain is reserved for advanced students, as are some of the standards in "the complex number system". In high school (Grades 9 to 12), the standards do not specify which content is to be taught at each grade level, nor does the Common Core prescribe how a particular standard should be taught. Up to Grade 8, the curriculum is integrated; students study four or five different mathematical domains every year. The standards do not dictate whether the curriculum should continue to be integrated in high school with study of several domains each year (as is done in other countries), or whether the curriculum should be separated out into separate year-long algebra and geometry courses (as has been the tradition in most U.S. states). An appendix to the standards describes four possible pathways for covering high