Though inquiry-based teaching has long been touted as an effective pedagogy, its application by elementary classroom teachers has been problematic. Two case studies were used to investigate effective professional learning experiences for teachers and the concomitant development of scientific proficiency in children. Both case studies used a newly developed instrument, the Classroom Observation Inventory, to collect data regarding teachers' use of the 5E model of inquiry-based teaching. The data indicates that teachers continually cycle through the stages of engage/elicit, explore, and explain with few teachers using the stages of expand/elaborate or evaluate. It is the recommendation of this study that the Classroom Observation Inventory and a newly developed 5E unit outline be used in conjunction with a variety of professional development scenarios as a collaborative data collection tool and discussion facilitator to support teachers in making informed instructional decisions that will enhance classroom practices to support students in reaching full science proficiency.