Diagnosis and treatment planning for periodontal disease are fraught with challenges because of the complex and multifactorial nature of the disease as well as the inherent variability in interpretation of clinical findings. It is important for all practitioners to be accurate and consistent in formulating diagnoses based on the American Academy of Periodontology classification guidelines and to implement treatment plans to adequately address patients' needs. The aim of this study was to compare diagnoses and treatment plans among four groups of participants: full-time and part-time periodontology faculty at Indiana University School of Dentistry (IUSD), full-time and part-time IUSD general practice faculty, full-time periodontists in private practice, and full-time general practitioners in private practice. The study, conducted September 2016 to February 2017, also sought to determine if the calibrated participants had more correct diagnoses and treatment plans than those who had not received calibration training. Each of the four groups had 20 participants each. Participants evaluated ten de-identified case records and selected a diagnosis and treatment plan for each case. In the results, the 20 IUSD periodontal faculty members, most of whom had participated in calibration sessions, had overall better agreement and more correct responses for diagnoses and treatment plans than the IUSD general practice faculty members, private practice general practitioners, and private practice periodontists (only one of those 60 participants had participated in calibration sessions). The results supported the notion that periodic calibration is needed to standardize faculty criteria, facilitate better agreement and accuracy, and enhance consistency in the use of clinical criteria during training for dental students and in practice.