The Invitational Teaching Observation Instrument was developed to extend effective teaching through self-assessment and clinical supervision. Based on the theories of Invitational Education, this test analyzed both personal and professional dimensions of teaching. Items reflected research on effective teaching and were cross-validated with two widely used teacher performance appraisal systems: The Assessments of Performance in Teaching Observation Instrument and the Teacher Performance Appraisal System. Data collected by two volunteer teachers provided case studies that demonstrated the use of the instrument in self-assessment and improvement strategies. Ratings from 17 observers who used the instrument to analyze a videotaped lesson indicated that while the general level of inter-rater reliability was adequate, 13 items yielded low inter-rater agreement. It was concluded that the Invitational Teaching Observation Instrument provides a valid and useful framework for self-assessment and, when revised to improve reliability, may provide a meaningful basis for clinical and collegial supervision. The Invitational Teaching Observation Instrument is appended. (Author/GDC)