A single-case multiple baseline design was used to evaluate the effects of supplemental mathematics instruction with Numicon on the number sense skills of kindergarteners with varying degrees of math difficulty. Nine students participated in the study. Intervention consisted of 20 minutes of supplemental mathematics instruction using the "Numicon Intervention Programme" over 10 consecutive school days. Data were collected using fluency measures of quantity discrimination and quantity-numeral correspondence, as well as a measure of general number sense. Student performance on the quantity discrimination measure and general number sense measure provided evidence of a strong effect. Furthermore, there was strong evidence of social validity indicating that both teachers and students felt that the intervention was effective and enjoyable. This study adds to the emerging body of number sense intervention literature. Educational implications are described emphasizing the role of screening and supplemental intervention in Response to Intervention frameworks. [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/en-US/products/dissertations/individuals.shtml.]