Selections from the last three basal reading series produced by the Houghton Mifflin Company were examined to determine what improvements were made. One of the fundamental changes occurring in the 1971 revision ("Readers") was the replacement of grade designations with numerical levels that provided a better match between student and materials. The 1979 revision ("Reading Series") switched from numerical to alphabetic levels, and also showed movement through preprimer levels instead of grouping all preprimers at one level. These 1971 and 1979 revisions reflected more realistic and equitable representation of minority groups, urban living, and a wider span of socioeconomic levels in their content than the 1966 "Reading for Meaning Series." More than half the 1966 selections were changed to add various literary styles, such as folk tales, jokes, biographies, poetry, and information selections. Interpretive and evaluative-creative questions were added to the predominantly literal types of questions proposed in the 1966 materials, thereby fostering critical and creative reading skills at early levels. More nonbasal words were included in the later revisions, though mastery of these words is not insisted upon. There was also a shift toward earlier instruction in reference and study skills, with application to content related materials. The 1979 revision made allowances for individual differences in ability by alternating instructional and reinforcing materials. (RL)