A situated cognition theory is presented in which situated learning is viewed from a Vygotskian perspective: the developmental situativity theory. It is assumed that learning is basically a non-symbolic inductive process that is greatly enhanced by formal systems which act as tools. Instruction should provide students with an environment containing elements to allow for situated activity as well as with appropriate formal tools. Tarski's World, which is an instructional Interactive Graphical Representation System in formal logic is an example of such instruction. The developmental situativity theory was supported empirically: Tarski's World was found to facilitate conditional reasoning, in contrast to instruction that is based on only-situa...