Kindergarten is emphasized as a critical first entry into the education system, as politicians and pundits believe kindergartners' success can lead to later academic achievement. Therefore, a comprehensive understanding of kindergarten school readiness data should consider how it is measured and how that affects learning. Using the Early Childhood Longitudinal Studies--Kindergarten (ECLS-K) cohort 2010-2011 data, the author examined the relationship between teacher reports about children's academic readiness at kindergarten entrance and their later outcomes in reading, math, and science through fifth grade. This study used a latent basis growth model with time-invariant predictors to analyze the relationship's trajectory. Overall, findings determined that teachers' perceptions of children's Approaches to Learning, mathematical thinking, and science significantly impacted later achievements in math and science direct assessments throughout elementary education. This research discussed the practice and policy implications on teachers' perceptions of school readiness and its impact on later academic outcomes.