The Reformed Teaching Observation Protocol (RTOP) was created by the Evaluation Group of the Arizona Collaborative for Excellence in the Preparation of Teachers (ACEPT) as an observational instrument designed to measure "reformed" teaching. This document is a guide to its use. The theoretical concepts that guided the development of the instrument are presented, as are reliability and validity information. In addition, the results of an exploratory factor analysis of the RTOP are presented. The RTOP, developed in 1998 and 1999, was used on all courses in the Fall 1999 evaluation of the ACEPT program. Results show that the RTOP is highly worthwhile in the study of mathematics and science classrooms in middle and high schools, colleges, and universities. With appropriate training, it is possible to achieve very high interrater reliability with the instrument. RTOP scores predict student learning in mathematics and science classrooms at all levels. Analysis of the RTOP suggests that it is largely a uni-factorial instrument that taps a single construct of inquiry. A finer-scale analysis lends new meaning to the phrases "pedagogical content knowledge: and "community of learners." The instrument seems to be able to measure what it purports to measure, reformed teaching. An appendix contains the RTOP. (Contains 17 references.) (SLD)