Offspring phenotypic variation can be substantially influenced by non-genetic factors such as maternal effects, which ultimately can influence organismal fitness. For oviparous organisms that lack parental care, oviposition-site choice and egg size are maternal effects that can greatly affect offspring traits. Yet, few studies examine the consequences of these traits in the wild. We manipulated the contents of natural painted turtle nests such that offspring spent two life stages (incubation and hibernation) in either maternally-selected nest sites or randomly-selected nest sites, and quantified treatment differences in environmental parameters and offspring phenotypes. Additionally, we tracked the fates of individual eggs and hatchlings, which allowed us to quantify the strength and form of selection acting on egg size during incubation and, for the first time, body size during hibernation. Maternally-selected nest sites were warmer and produced offspring that were longer and hatched earlier than their siblings emerging from cooler, randomly-selected nests. Treatments did not affect any measured traits during hibernation. We detected no selection on egg size during the incubation stage, but significant linear selection favoring larger hatchlings during hibernation. Our results suggest that nest-site choice allows mothers to partially control the environment of their incubating eggs, but is less effective at controlling hatchling environments during hibernation. Additionally, we provide novel support for the “bigger-is-better” hypothesis in turtles by showing a positive relationship between size and survival during the hibernation stage.