This study developed and validated the School Counselor National Model Activity Scale (SCNMAS) to assess implementation of the American School Counselor Association (ASCA) National Model. Data was collected through an online survey of over 1,000 school counselors. Psychometric analysis found the SCNMAS to be reliable and valid. It differentiated levels of implementation based on counselors' experience. The SCNMAS measures three factors: management, delivery, and themes. Researchers conclude it can help evaluate and improve comprehensive developmental school counseling programs.