This article is about one school district's effort to reform its elementary science curriculum through a program of professional development called Science, Parents, Activities and Literature (Science PALs). The differential exposure of the district's K-6 teachers to Science PALs and differences in how well teachers implemented Science PALs-type inquiry strategies allowed us to conduct a quasi-experimental study of the impact of Science PALs on student achievement and attitudes. We measured achievement with an instrument based on items taken from the "Third International Mathematics and Science Study" (TIMSS; International Association for the Evaluation of Educational Achievement, [1997]) and selected attitudes about science with the "Student Perceptions of Classroom Climate" (SPOCC; Yore et al., [1998]), an instrument that we designed. Our analyses of student attitude scores as a function of years of teacher participation in Science PALs and supervisor's rating of a teacher's implementation of the project's instructional approaches showed a significant overall positive impact on student attitudes toward school science. Student TIMSS scores on multiple-choice items or constructed-response items did not improve significantly when analyzed by the number of years a student's teacher was involved in the Science PALs effort or by the supervisor's rating of that implementation. We found no significant differences in attitude or achievement scores among students taught by a series of teachers rated high, medium, or low in quality of implementation by the district's science supervisor. We discuss possible explanations for the lack of clear and positive connections between Science PALs and student performance in light of the increased focus on accountability in reform projects.