As a RDA for sixteen years or so and a current ETSU dental hygiene student, I know first hand that assistants do not get the formal training or education that is necessary to scale teeth.  It is in the best interest of the patient to not allow assistants to scale.  There is a whole lot more that goes into it than just scaling on the teeth.  Damage can be done to the patient's teeth and/or gingiva.  Please do not allow this to happen.  Assistants are an important part of the dental team, but scaling should be left for the educated dental hygienist.  Their is a tremendous amount of education and traing that goes into learning the proper way to scale teeth.  Leave scaling to those who have the expertise to do so.