In this paper, we examine the validity and precision of two nonexperimental study designs (NXDs) that can be used in educational evaluation: the comparative interrupted time series (CITS) design and the difference-in-difference (DD) design. In a CITS design, program impacts are evaluated by looking at whether the treatment group deviates from its…

There are several goals guiding this study. First, the authors use an experimental design to examine the causal effects of giving children 10 self-selected books over two summers. Second, they examine whether treatment effects are moderated by children's family income (i.e., eligibility for free- and reduced-price lunch). As a result, they examine…

Despite its apparent simplicity, random assignment is an abstract concept for many students. This article describes a classroom demonstration that uses a standard deck of playing cards. In small groups, students randomly assign playing cards (i.e., participants) to 2 treatment groups. Following randomization, students compare the relative…

Expresses the importance of scientifically based research in education reform and explains how to judge the validity of educational research. Describes control groups, randomized and matched experiments, statistical educational significance, sample size, and the difference between scientifically based and rigorously evaluated research. (Contains…

Background: Multiplication and division by fractions are among the most troublesome concepts in the elementary mathematics curriculum. Recent studies have shown that preservice elementary teachers in the United States do not have deep understandings of these concepts. Effective ways to improve preservice teachers' conceptual understanding of these…