COMAR Basics
The requirements for Maryland's public schools are governed by the Code of Maryland Regulations (COMAR). While the regulations set out in this code do not have attached legislation that requires their funding, they lay out what Maryland public school students are legally entitled to in their education, and what the state high school graduation requirements consist of. Below is the COMAR regulation about arts education. Note that these are not supplemental courses, and that an arts credit is required to graduate.
Here is the relevant text of COMAR as a graphic

Here is the relevant text of COMAR in text form:
The Fine Arts in the Code of Maryland Regulations (COMAR)
.01 Requirements for Fine Arts (Dance, Media Arts, Music, Theatre, Visual Art) Instructional Programs for Grades Prekindergarten –
2A. Each local school system shall:
(1) Provide an instructional program in fine arts each year for all students in grades prekindergarten—8 as follows:
(a) Within the prekindergarten—5 grade span, students shall have experiences in the fine art forms of dance, media arts, music, theatre, and visual art; and
(b) Within grades 6—8, students may specialize in one or more of the fine art forms of dance, media arts, music, theatre, and visual art; and
(2) Provide an instructional program that enables all students in grades 9—12 to meet graduation requirements, and to select from among fine arts elective courses of dance, media arts, music, theatre, and visual art that will prepare them for post-secondary education and careers.
While the regulation uses the word "elective courses" (.01.2A.2), this is slightly misleading. These courses are still required, but students may elect from a set of options of all five of Maryland's fine arts disciplines. The courses are not elective and students are required to have access to courses in Dance, Media Arts, Music, Theatre, and Visual Arts.
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