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Nearly 14% of students in the United States receive special education services in public schools (NCES, 2017). Special education programs serve students with a wide range of developmental differences and vary considerably across schools and districts (National Research Council, 1997). Likelihood of identification for special education services also varies by gender, race, ethnicity, and socioeconomic status. Identifying sources of variation in special education identification, and in the placements of students once identified, has driven a wide body of work in multiple fields (e.g., Elder, Figlio, Imberman, & Persico, 2019; Hibel, Farkas, & Morgan, 2010; Skiba et al., 2006). Just as student demographics are associated with likelihood of special education placement, students who are younger than their peers when they start school are more likely to be identified with disabilities (Elder, 2010; Evans et. al, 2010; Layton et. al, 2018) and placed in special education (Dhuey, Figlio, Karbownik, & Roth, 2019; Dhuey & Lipscomb, 2010). Differences in special education identification and placement types may impact the outcomes of students who do or do not receive special education services and the school districts that operate these programs. This dissertation includes two stand-alone manuscripts on the relationship between age and special education identification and placement. In the first study, I used a regression discontinuity design using a statewide kindergarten entrance policy in Michigan to estimate the effect of being young for grade on the likelihood of receiving special education services in each elementary and middle school grade. I find that the youngest kindergarten enrollees were 3.3 percentage points (40%) more likely to be identified for special education in kindergarten than their oldest peers. I find no evidence of heterogeneity in the effect of school starting age by gender, race, or socioeconomic status, and no evidence of heterogeneity across school districts in Michigan. I also find exploratory evidence that these effects are driven by relative age comparisons rather than absolute age differences between students who start school a year apart in age. In the second study, I describe the disability classifications, service prescriptions, educational settings, and likelihood of special education exit for students who are placed in special education at different ages in the same grade. Within school, year, and grade of placement, I compare the special education characteristics of students who are in the youngest third, middle third, and oldest third of their cohort by age. I also estimate these differences with and without students who are older than expected for grade due to delayed school entry or grade repetition. I find that the younger students in kindergarten are more likely to be placed for milder impairments and to exit from services whereas the oldest students have more severe disability classifications and are less likely to exit into general education, particularly those who are older than expected for grade. The findings from this dissertation add new evidence that starting school at a younger age increases the likelihood a child receives special education services and that the types of placements students receive varies considerably within grade by age. They also motivate future research evaluating the impact of earlier identification for special education services. Finally, they have policy implications for the special education referral and evaluation process, kindergarten enrollment practices, and grade retention for students with disabilities.