The use of kits in elementary science classes is a growing trend in some countries. Kits provide materials and inquiry lessons in a ready-to-teach format for teachers to use in their science instruction. This study examined elementary teachers' instructional strategies, classroom practices, and assessment types in relation to the frequency of science kit use. A total of 503 elementary teachers from an urban school district received professional development, implemented kits in their classrooms for a year, and then completed a survey about science kit use and teaching practices. Despite similarities in demographic characteristics (gender, ethnicity, certification/educational level), there were significant differences in teachers' use of inquiry-based teaching and assessment practices by kit use. Teachers who reported using kits the most often were significantly more likely to report that their students designed and implemented laboratory investigations as well recorded, represented, and analyzed data. In addition, the high kit users indicated that they were more likely to use student groups, require students to use evidence to support claims, and use alternative assessments of student work including portfolios, notebooks, and long-term projects than those teachers who used kits less frequently. Those teachers who reported using kits the least often were significantly more likely to report having students practice for standardized tests. The role of kits in promoting reform-based teaching practices is discussed.