The heuristic model and measurement models guiding a proposed seven-year investigation of how children learn to comprehend what they read--and in particular how they comprehend science text--are described in this report. The report first offers a brief description of the heuristic model, which is based upon and extended from studies of effective teaching and includes eight constructs: (1) the abilities possessed by students entering school; (2) instructional materials; (3) classroom management; (4) instructional feedback; (5) instruction in decoding, comprehension, and science; (6) stable home characteristics; (7) home support for literacy and science knowledge; and (8) student ability at the end of kindergarten. The remainder of the report discusses and presents empirical support for the measurement models built for each of the constructs. References, figures and a table of effective behaviors in four stages of instruction are appended. (FL)