Determining the Impact of Applet-Based Instructional Materials on Teacher Knowledge of Content and Pedagogy, Instructional Planning, and Student Learning of Fractions Report of Preliminary Research Findings1 Karen Wetherill Watson School of Education University of North Carolina at Wilmington Wilmington, North Carolina 1. First Phase This paper describes the preliminary findings of the first phase of a two-part study on the impact of NCTM E-Standards and Illuminations applets and support materials on teacher knowledge of mathematics content and pedagogy, instructional planning, and students’ learning of fractions. This qualitative study is designed to describe how teacher’s knowledge and practice changes as a result of using the “Fraction Track” applet as an instructional tool and document examples of student learning. Early findings from phase one indicate that teachers learn the “big mathematical ideas” that are foundational to concept development for students’ understanding of fractions. The middle grades students were motivated to learn and saw new relationships with these electronic representations. Also, results indicate an increase in teachers’ understanding of the relationship of pre-requisite knowledge about part-whole relationships and their ability to teach the addition and subtraction of fractions. 2. Second Phase The second phase will continue studying the subjects in the first phase to collect formative data on the design of the applet-based resources and to engage the subjects in creating resources for the Illuminations website. In addition, phase two of the study will document the value of applets for upper elementary teachers and students and determine the impact of such on-line resources on improving instructional knowledge of lateral entry teachers, who are entering the profession with mathematical content knowledge applied in a context other than teaching. See Equation (1):