i Acknowledgements I would like to thank my adviser, Dr. Kristen McMaster. Before Kristen was my adviser, she was my doctoral seminar instructor, and in that capacity she provided thoughtful and constructive feedback that made me a stronger writer and a more critical thinker. As my adviser she effortlessly displayed kindness and respect, two qualities that I strive for in my professional and personal relationships.I first applied to graduate school at the University of Minnesota to pursue a degree in school psychology, and at that time I began working with Dr. Ted Christ. While working alongside him I developed an excitement for research. Although I did not continue pursuing a degree in school psychology, Ted did not give up on me as a student and continued to advise me; for that, I am grateful. I would also like to thank Dr. Michael Harwell for sharing his expertise and allowing me to learn from him. I am also extremely grateful to Dr. Michèle Mazzocco, who modeled professionalism and set high standards for research. I gained invaluable skills and knowledge while working in her research lab. I hope to transfer these skills to my own research and mentoring of future researchers.Finally, I would like to acknowledge my writing group members, Steph Brunner, Jessie Kember, and Chloe Webb. Friendly competition, accountability, and monthly social evenings made it easier to see the light at the end of the tunnel.ii Dedication I dedicate my dissertation to my parents and my grandmother. I consider myself incredibly lucky to have parents who have always supported me as I have pursued my dreams. From the time I was a child, they set high expectations and taught me to value hard work. I am grateful to my dad who expects me to "do things right the first time," but also to my mom, who is always there to remind me that it is okay to make mistakes. I also dedicate my dissertation to my grandma Amy. She was tenacious and was never afraid to vocalize her opinion. I attribute my strong-willed nature and my "never give up" attitude to her; two qualities that I know got me where I am today.iii Abstract The purpose of this meta-analysis was to examine the effectiveness of early numeracy interventions for young students, including students with disabilities or those at-risk for mathematics difficulty (MD). This study evaluated preschool, kindergarten, and first-grade interventions on early numeracy content, instructional features, and methodological components that improved students' mathematics achievement. A total of 33 studies met inclusion criteria for this meta-analysis, with 51 treatment groups. Excluding outliers, the average weighted effect size for numeracy interventions across 49 treatment groups was moderate (g = 0.63), and the 95% confidence interval did not include zero [0.50, 0.73].Results indicated that early numeracy interventions that included preschool and kindergarten students produced larger treatment effects than interventions with first-grade participants; in addition, treatment effects were slightly higher on av...