Voluntary Work

Volunteer or unpaid work is also explicitly prohibited for dependents, and it probably says that on your iqama.  I haven't seen a dependent's iqama lately, but when I was growing up here, the iqamas used to be booklets, like passports, and I clearly remember one of the pages in my iqama saying that working, including unpaid work, is not allowed.

So yes, if the place was raided, you and the employer both, could get into trouble, probably not as severe as someone working for pay, but then again, you don't want to test what the authorities will do.

Having said that, if you are on personal terms with the potential employer where you want to do volunteer work, go ahead.  But make sure that you have a serious conversation with your employer about exit strategies in case the inspectors come to check.  If it is a school, it would be very easy for you to sneak out of the classroom and pretend to be a parent who has come to see your child's teachers/principal.