The study of cognitive development has often been framed in terms of the nativist/empiricist debate. Here I present a new approach to cognitive development – rational constructivism. I will argue that learners take into account both prior knowledge and biases (learned or unlearned) as well as statistical information in the input; prior knowledge and statistical information are combined in a rational manner (as is often captured in Bayesian models of cognition). Furthermore, there may be a set of domain-general learning mechanisms that give rise to domain-specific knowledge. I will present evidence supporting the idea that early learning is rational, statistical, and inferential, and infants and young children are rational, constructivist learners.