In order to study why students have difficulty learning from science textbooks, this study investigated how middle school students use textbooks and how their thinking about one science concept (photosyntheis) was influenced by the reading of three different science texts. One of the texts used was an experimental one written to challenge and change students' common misconceptions about how plants get their food. The other two texts were commercially available texts covering the same content as the experimental text. Daily interviews were used to trace the thinking of students (N=18) as they read one text chapter over a 3-day period. This approach provided detailed information about the cognitive lives of students during textbook reading that has important implications for understanding learning processes, teaching, and textbook development. A unique part of the study was the exploration of conceptual learning from text. Findings, among others, show that both "good" and "poor" readers have difficulty learning from text because they use ineffective text processing strategies and that only students using a conceptual change strategy for processing text were successful in giving up or modifying their incorrect prior knowledge in favor of text explanations. (JN)