Children from low-income families often begin kindergarten at an academic disadvantage. This research consisted of a causal comparative study of the short-term and longer term academic effects of voluntary prekindergarten (VPK) participation with a population of students who qualified for free or reduced-price lunch in a large southern public school district. Reading and math achievement of low-income students who attended VPK in 2008-09 were compared with a matched sample of students who did not attend. Incremental changes following the 2008-09 prekindergarten year to the cohort’s and matched sample’s 2012-13 third-grade academic performance were compared via archived kindergarten, first-, second-, and third-grade test scores, ratings, and promotion status at the end of third grade. Additional analyses were made to test for any differences between program length for the VPK and non-VPK attenders. Analyses were also conducted to see if the effects of VPK persisted through the early school years as measured by school type (Title I or non-Title I). Short-term and longer term effects in favor of VPK participation were found for kindergarten, first, and third graders who attended summer or full-year programs and a Title I school for 1 to 3 years of their academic career during the 4-year period examined. However, those students who attended VPK but who did not attend any Title I school from kindergarten to third grade did not perform better statistically than matched students who did not attend VPK. It is recommended that full-year prekindergarten programs be considered for students likely to attend high-poverty schools. Reading readiness and achievement were significantly higher for the students attending high-poverty schools if they previously attended full-year prekindergarten programs.