Can't go wrong with braids. Always found it odd they used it as a stereotypical 'plain girl' look in some series b/c i think it's more 'effort' to put your hair into two braids as opposed to brushing it straight or a single ponytail lol
(dang i'm sure it'd be helpful or so but i feel like the concept of an 'apology letter' could lead to like some annoying sensei abusing their power or something lol, not that actual troublemakers would bother doing it but eh)