Physiologically acclimation to temperature change is hypothesized to evolve in environments with high levels of temperature variation. However, this hypothesis has low explanatory power, meaning other factors must be in play. Behavioral thermoregulation can reduce the body temperature variation that organisms experience and selection on thermal physiology (the “Bogert Effect”). However, the interplay between behavioral thermoregulation and the evolution of thermal acclimation is rarely discussed. I will describe how the Bogert Effect applies to thermal acclimation, and use lizards as models to provide examples of how thermoregulation reduces seasonality in body temperatures and performance relative to null expectations from environmental data.