This study investigated the reasons behind the lack of enthusiasm among teachers in implementing a new biology curriculum in Israel. Classroom observations of 42 junior high school teachers in 28 schools revealed that the curriculum developers succeeded in transmitting most of their curriculum objectives. The data indicated three possible reasons, however, for teachers' disappointment: (a) The high expectations set at the ideal level regarding the inquiry approach; (b) The greater role given to verbalization in a biology curriculum, and (c) Dull implementation (routine and nonenthusiastic), which occurs when teachers are too faithful to the teaching text. Four variables—objectives, materials, strategy, and activities—were chosen in order to analyze the learning materials. The variables, and their sub-variables, were scored in terms of the ideal, formal, and operational levels of the curriculum. To score the qualitative implementation data, two new instruments were developed. The first, an analytical instrument, analyzed instructional materials in terms of the frequency and intensity of their use. The second instrument, an observational one, was used to estimate classroom implementation fidelity.