Are virtual manipulatives as effective as concrete (hands-on) manipulatives in building conceptual understanding of number concepts and relationships in pre-service middle grades teachers? In the past, the use of concrete manipulatives in mathematics courses for Clayton State University's pre-service middle grades teachers has been effective in building conceptual understanding of a variety of mathematical topics. This paper presents the results of a three-year study in which 78 middle grades mathematics teacher candidates used various concrete and virtual manipulatives to study fractions, integers and nondecimal-based numbers. They then compared each type of manipulative for ease of use and helpfulness in understanding the concepts addressed.