“…Indeed, models of normal arithmetical development have been successfully used to guide the study of MD children, and have revealed at least two sources of MD. These include disrupted memory-retrieval processesdifficulties retrieving basic arithmetic facts from long-term memory-and the error-prone use of developmentally immature problem-solving procedures (Ackerman & Dykman, 1995;Barrouillet, Fayol, & Lathulière, 1997;Bull & Johnston, 1997;Bull, Johnston, & Roy, 1999;Garnett, & Fleischner, 1983;Geary, Brown, & Samaranayake, 1991;Geary, Widaman, Little, & Cormier, 1987;Jordan, Levine, & Huttenlocher, 1995;Jordan & Montani, 1997;Ostad, 1997;Räsänen & Ahonen, 1995;Rourke, 1993;Russell, & Ginsburg, 1984;Svenson & Broquist, 1975).…”