Activity-based instructional strategies promote physical interaction with manipulatives to represent abstract concepts. As a means to improve student achievement in mathematics, educational researchers and practitioners often recommend instructional strategies that capitalize on the assumed benefits of manipulatives. Recent research has indicated that instructional context and type of manipulative moderate the effectiveness of manipulatives (Carbonneau, Marley, & Selig, 2012). To better understand the instructional environment that must be present in order for manipulatives to be effective the present study examines the relationships between two instructional characteristics: level of instructional guidance offered to students and the type of manipulative used during learning. Results from the randomized experiment with preschool children (N = 72) indicate that the use of math manipulatives is most effective when integrated in instructional guidance scenarios that offer high levels of support for student learning. In addition, depending on level of instructional guidance and learning outcome, realistic manipulatives had differential effects. Specifically, students who manipulated realistic manipulatives performed worse than those who utilized bland manipulatives when measured on their conceptual knowledge, however, students who manipulated realistic manipulatives were better able to transfer their knowledge to a number line representation. This finding highlights the need for additional research in how realistic manipulatives impact student learning. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]