AbstractBackgroundInferences about cognitive reserve and related constructs may be subject to reverse causation, but too often the possibility of reverse causation is not addressed in research on reserve and resilience. A lifespan perspective can shed light on the relationships among education, IQ, and related constructs and what can be concluded about causality with respect to late‐life cognitive and dementia outcomes.MethodWe use general cognitive ability (GCA) to refer to IQ or IQ‐like measures. We provide examples from the literature plus some new findings examining the effect of cognitive reserve on late‐life outcomes and how modifiable factors may impact reserve and resilience effects. Some of the data presented are from genetically‐informative studies that help to clarify issues related to causality.ResultThere is a bidirectional relationship between education and GCA, but the directional influences change across the lifespan. The relationship is not unidirectional in childhood and adolescence, but during that period more education does increase GCA. The effect reaches an asymptote, and in late adolescence and early adulthood, the causal direction shifts toward GCA driving educational attainment. When both education and GCA are in the same model, both longitudinal phenotypic and Mendelian randomization studies show that GCA is a stronger driver of late‐life cognitive and dementia outcomes than education. Appropriately designed studies often support the idea that occupational complexity and engagement in enriching activities are not directly causal, but are downstream effects of GCA. Finally, earlier lifestyle factors can moderate associations between cognitive reserve and late‐life outcomes. For example, favorable early midlife social/health behaviors can offset advanced brain aging in individuals with lower cognitive reserve (i.e., lower young adult GCA).ConclusionThe results have implications regarding interventions to improve cognitive reserve and resilience, and what the balance should be when it comes to resources for early‐ versus late‐life interventions. The primary direction of causal effects raises questions about how and, importantly, when during the lifespan, increased education, cognitive enrichment/training programs (which may be thought of as a type of education), or other lifestyle factors are likely to increase reserve or resilience, thereby improving cognitive function and reducing dementia risk.