Have you experienced being added to a Facebook group without your consent? Unfortunately, there is no setting that would let you approve group membership or prevent people from adding you to a group.
Do remember that just like being tagged in a picture, only people from your friends’ list can include you to a Facebook group. However, school groups let users to add people in their school community even if they are not on their friends’ list. Moreover, once you are added to a group, you will receive a notification right away.
Good news is you can leave the group any time you wish to. Additionally, once you decide to leave a group, you can’t be added to the same group unless you specifically request to be re-added.