This article discusses early age flexural strength development in concrete, specifically investigating the role of aggregates and their impact in maturity predictions. The maturity method is becoming more widely used by the construction industry to signal when certain construction operations (e.g., opening to traffic or removing formwork) can be performed. In addition, the maturity method is used in various computer programs to simulate how physical properties develop during hydration. The maturity method is based on the concept that strength (or mechanical property development is proportional to the extent of chemical reaction (i.e., hydration) that has taken place. It is commonly assumed that the extent of chemical reaction (i.e., the degree of hydration) is a unique function of the product of lime and temperature. It is the hypothesis of this work that aggregates can alter this relationship specifically influencing the early age relationship between maturity and flexural (or tensile) strength. To verify this hypothesis the nonevaporable water (i.e., the degree of hydration) was related to the flexural strength development in paste, mortar, and concrete specimens. A linear relationship was observed between the flexural strength and the nonevaporable water for paste specimens, while a bilinear response was observed for both mortar and concrete. The knee point of this bilinear behavior corresponds to the time at which the majority of the aggregates begin to fracture. At very early ages (i.e., less than 2.5 days in this study) the flexural failure behavior is dominated by the paste or bond failure, while at later ages flexural failure is dominated by aggregate failure.