At the very least, it'll help teach good habits? Sylvia may already know about hand washing, but I bet not all her classmates (and parents) do it enough. This is somewhat heartening, a real common sense health precaution thing that works!
She can go home and eat dirt after school :)
Dirt is good. Dribbles at school are not!
Lukas' school has always had "wash hands on arrival" as an enforced rule for the kids but generally unenforced for parents. It is now enforced for everyone. :)