The science achievement of 226 5th graders from districts that have a kit-based inquiry science curriculum supported by intensive professional development (PD) is compared with data from a group of 173 5th graders from other districts that use nonkit science materials and do not have systematic science PD for teachers. Within the kit-based project, the sample of project teachers is stratified to select teachers with a high number of science PD hours versus those with few hours. While there were no significant differences in the mean total scores for kit-based students with low PD versus high PD teachers, the kit-based classrooms scored significantly higher than students in nonkit classrooms on both the pretest and posttest, though there were significantly more minutes of science instruction in the nonkit classrooms. Finally, nonkit teachers taught more units of shorter length and reported lower levels of preparedness to use reform pedagogical approaches.