Please do NOT allow assistants to scale teeth.  There is already a position for that duty, the Registered Dental Hygienist.  By allowing an assistant to scale, you will be compromising not only quality of care, but the health and wellbeing of patients.  There is a reason that Dental Hygienists spent at least 2-4 years of college studying the profession.  Is an assistant qualified to do the same because he/she has an extra hour of lecture added to their training? No.  Absolutely not.