dress code is a big problem I know it sounds like taking the easy way out just make them were school uniforms trust me it sounds great in in all but there is a different way out of it an it's easy too just hear how simple it is. you may just need to set some different rules or stricter rules down and that's all you need to do and if that does not work then you may want to resort to some uniforms.
you also may need to think about the parents money