JW like black/white good/bad rules. Not too much into thinking and deciding. So you're right about nothing being written explicitly on the subject, it's easier to 'decide' the anything that is not formal classes is not appropriate.
Many frown upon my wife and I, because we let our kids go in field trips, we attent every PTA, parents night or event the school holds. Our ccrodinator even got mad at me because I asked him to cinduct TMS for me, because I had a 'parents night' at my son's school. He won't confornt me because I'm a feared and respected elder, but he told me "You know attendance is not mandatory for those things?", to which I replied "Neither is mandatory for TMS".
But what can I say, my kids come first!