Much has been written about the value of metacognition. However, little research has identified subsumed intellectual factors, logical operators, and cognitive functions; or has established clear relationships between metacognition and science cognition. This paper presents a study to build a strategic metacognitive model of an efficient, successful science reader based on research results. Other goals are to develop an objective assessment instrument, to validate the instrument, and to provide a profile of middle school students' metacognitive knowledge about science reading and science text. The objective test and interview protocols were developed based on a matrix associated with a theoretical model that crossed 21 comprehension strategies with 3 levels of knowledge: declarative, procedural, and conditional. The objective tests were validated using a group of 532 volunteer students from grades 4 (n=113), 5 (n=108), 6 (n=109), 7 (n=93), and 8 (n=109), and the interview protocols with a random selection of 52 students from those groups. Factor analysis of the students' responses to the objective test generated a metacognitive profile of middle school students' knowledge about science reading and science text. Results of the profiles indicated: (1) surface level declarative, procedural, and conditional knowledge for middle school students on the factors tested; (2) significant differences between high ability readers and low ability readers; (3) a gender difference favoring girls; (4) no increase in metacognitive awareness of science reading and science text in middle school students with additional years of schooling; (5) significant differences between metacognitive domains; and (6) specific strategies that regard reading as an interactive-constructive process. (Contains 14 references.) (MDH)