A model for developing instructional analogies was used to produce experimental treatments that included text from a high school biology textbook to which was added extended verbal analogies written by the researcher linking each of two biology concepts to analogous familiar concepts. The control treatment was text from the biology textbook retyped in the same format as that of the analogy text. Students randomly assigned to experimental or control treatment within each of nine classrooms read the texts on the topics of evolution and cellular respiration and took immediate and delayed recall content achievement tests. Results included significant differences in biology achievement in favor of the analogy treatment group on the immediate recall test on the evolution topic and on the delayed recall test which covered both topics. An achievement difference on the immediate recall test of the respiration topic, while in favor of the analogy treatment group, was nonsignificant. Teachers and textbook authors are encouraged to use the parts of the model supported by the results of this study for developing effective instructional analogies. (Author)