The Developmental Supervisory Competency Assessment System presented in this guide has been developed for use in the diagnostic analysis of the competencies of school personnel in instructional supervision. The system, intended for voluntary use by individual supervisors interested in professional self-improvement, combines self-assessment features with descriptions of performance from other, external sources. Over 200 instructional supervisory activities are specified and clustered into 36 competency statements. These statements are clustered in their turn into nine task areas: developing curriculum, providing materials, providing staff for instruction, organizing for instruction, relating special pupil services, arranging for inservice education, developing public relations, providing facilities for instruction, and evaluating instruction. Utilization of the system involves a four-phase process for selecting a task area to analyze, involving others in identifying specific competencies needing attention, determining specific performance activities needing work, and planning for developing ability in those performance areas. The material collected in this document includes a description of the system and its use, detailed specifications of the competencies covered, simulated responses (provided as examples) to the three instruments used in the system, and blank copies of the three instruments along with directions for their use. (Author/PGD)