The purpose of this study was to investigate the effects of formative assessment as a teaching strategy through an internet-mediated assessment portal (ImAP) on preservice elementary student understanding of kinematics graphs as opposed to traditional lecturing. A quasi-experimental design was used for this purpose. Findings revealed that students' post-test mean scores were statistically significantly higher than their pre-test mean scores. Moreover, the ImAP-taught students' post-test mean scores were significantly higher than the control group students' post-test mean scores. However, Hake's average gain index classified both treatment methods as medium effective. For both treatment methods no gender differences were found in students' understanding after instruction. (Contains 4 tables.)