I'd say that it's more "harmful" than helpful. Most students today procrastinate so giving them studyhall probably won't accomplish much and wastes learning time.
If you need help I recommend you type in the specific question you need help with
Study
it can be helpful or harmful
sometimes they are helpful and harmful.
Sandpaper is both helpful and harmful.
they are helpful not harmful to plants
helpful
helpful
Depends on what part of "harmful" or "helpful" you are referring to.
Harmful bacteria will harm you. Helpful bacteria will help you.
Slash and burn does not sound helpful, it sounds harmful.
helpful