On its face, the policy clearly does discriminate based on sex, and thus seems like a facial violation of Title IX and a presumptive violation of the Equal Protection Clause (since the kindergarten is a public charter school). But courts in employment discrimination cases have long upheld certain kinds of sex-differential grooming policies, such as hair length policies, so long as both men and women are subjected to standards that are seen as socially accepted for their sex. Here is an excerpt from Hayden ex rel. A.H. v. Greensburg Community School Corp. (7th Cir. 2014), the precedent on which the plaintiff chiefly relies, which struck down a male-only hair-length limit for a high school's baseball and basketball players:

Presumably in this case, the school will indeed argue that its policy provides extensive grooming rules (albeit not identical ones) both for boys and for girls:

Appropriate undergarments must be worn and not visible. Camis for girls and undershirts for boys are allowed, but not required, and must not show. Make-up may not be worn until the 7th grade and must be conservative in nature. Tattoos and body piercings, other than girls' earrings, are not allowed. Earrings must be limited to 1 earring per ear. Large, dangling or hoop-type earrings are not allowed. Jewelry other than watches for boys or girls, and small earrings on girls, may not be worn. This includes bracelets. Bracelets are not allowed. Official RMCA bracelets are allowed to be worn. Necklaces may be worn but should be inside the shirt. Hairstyle and hair color must be conservative in nature. Boys' hair must not extend below the top of the shirt collar in the back, the bottom of the ears on the sides or the eyebrows in front. Mohawk, faux hawk, no symbols, shapes or designs of any kind shaved into the head or anything that inhibits the learning environment as determined by the campus principal. Hair may not be spiked. Large hair decorations may not be worn. Bandanas may not be

worn. Highlights must be two tones lighter or darker than the student's natural hair color. No highlights that are not a natural hair color. No pocket chains or hats may be worn in the building.

And the Supreme Court's pending case on whether gender identity discrimination violates Title VII may ultimately affect the analysis as well, depending on what reasoning the Court endorses. You can read the plaintiff's motion for a temporary restraining order, and here's the school's public statement in response (its legal arguments have not yet been filed):