They changed the dress code partway through a school year in a way that specifically targeted both him and another black student.

Are the girls held to the same standards?

Black hair often tends to be more coarse, dry, and curly than others' hair. A lot of black hairstyles are meant not only as source of self expression, but also to promote moisture retention, scalp health, and cleanliness since frequent washing can easily strip oil from the hair and damage it. It also helps protect the long but brittle hair against breakage.

Unfortunately, there's a long history of black hair styles being seen as "messy" and "unprofessional" in the US, owing to our colonial past. Many people don't really understand black hair care and believe the same rules apply to all kinds of hair, requiring or at least implying that hair should be relaxed/straight in a professional setting and anything else looks "nappy", unkempt, or "ghetto".

This is the feeling we get when seeing the rule about length when hair is "let down", the idea that, should George not wear this particular style, his hair would hang down to his shoulders. That's just not how that kind of hair works, so why is that kind of measurement being applied? "Length" is not deterministic for that kind of hair (ever seen someone before and after they pick their hair?) so the rule seems rather arbitrary. Is this rule applied equally to students with looser curly hair that naturally sits above their hairline when, if straight, it would drop over their eyes? How about people who wear a fro that can be pulled down to their shoulders? His hair is not to his shirt collar or over his ears, nor could it easily become so during the school day, so what exactly is the problem with it? It feels like this rule has been arbitrarily enforced in this case not because of the length of his hair, but because of the particular style of it. Intentional or not, it smacks of some of those old (but still prevalent) conceptions about certain traditionally black hairstyles.