The effects of age/maturation, grade, amount of school exposure, and early or late entry into school, on mathematics and executive function skills of pre-kindergarten and kindergarten students was examined. The sample consists of four-and five-year olds from low-income ethnic minority families enrolled in pre-kindergarten (pre-K) (n = 42) and kindergarten (n = 40). Assessments of mathematics competency and executive function were conducted by trained researchers in the fall of the school year. Regression analyses were conducted to test the effects of age/maturation and amount of schooling, while independent samples t-test were used to examine late versus early entry into school, the value of pre-K attendance, and if grade level matters. The findings revealed that there is a maturation effect to an extent in the beginning of the preschool year. The importance of school exposure (pre-K attendance) and early entry was also confirmed. A future longitudinal study needs to be conducted that follows the same cohort from pre-K to adulthood in order to find the long term effects underlying this debate.