Constructivism is a theory of knowledge that asserts that individuals actively construct or make their own knowledge and that reality is determined by the experiences of the learner. Learning is an active process in which the learner constructs new ideas or concepts based on both their current and past knowledge. The learner selects and transforms information, constructs hypotheses, and makes decisions using their cognitive structure. An example is given of an elementary school teacher allowing students to use their own methods to measure the length of the Mayflower rather than introducing a ruler.