Wis. Stat. § 118.145: Admission to high school.

(1) The school board of a district operating high school grades shall determine the minimum standards for admission to high school.

(2) A certificate or diploma or other written evidence issued by a school board showing that the pupil has completed the course of study in the elementary grades of the school district in which the pupil resides shall entitle the pupil to admission to high school. Such certificate or diploma or a certified copy thereof or a certified copy of a list of graduates shall be filed with the school district clerk of the school district operating the high school.

(3) If the superintendent of a private school or of a tribal school files with the department the course of study for elementary grades prescribed by such school and if such course of study is substantially equivalent to the course of study prepared for elementary grades by the department, a certificate or diploma or other written evidence issued by the superintendent of the private school or tribal school showing that the pupil has completed such course of study shall entitle the pupil to admission to a public high school. The certificate or diploma or a certified copy thereof or a certified copy of a list of graduates shall be filed with the school district clerk of the school district operating the high school.

(4) The school board of a school district operating high school grades shall allow a pupil enrolled in a private school or a pupil enrolled in a tribal school, who has met the standards for admission to high school under sub. (1), to take up to 2 courses during each school semester if the pupil resides in the school district in which the public school is located and if the school board determines that there is sufficient space in the classroom.