The purpose of this study was to describe how providing teachers with research based knowledge about developmental throwing can influence teachers' observational interpretations and their students' practice patterns. Eight kindergarten classroom teachers with high generic teaching skill competence taught a 6-week overhand throwing unit to the children in their intact classes. Prior to the unit, four of the teachers were randomly assigned to a 4-hour knowledge training program. The other four teachers served as a comparison group (underwent no knowledge training). During the unit, data from stimulated recall interviews were used to describe and compare the thoughts and knowledge concepts expressed by the two groups of teachers. The throwing practice experienced by the children in the knowledge-trained and comparison teachers' classes was videotaped and analyzed for frequency of opposite foot stepping. The knowledge acquired during training was associated with different patterns of skill observation. The knowledge concepts the teachers acquired during training formed the basis of many of their thoughts and were reflected in the instructional procedures implemented. The knowledge-trained teachers' classes demonstrated more than twice as many opposite foot throws during the unit than the comparison teachers' classes.