Several educators have also questioned the effectiveness of this approach toward instructional design, especially as it applies to the development of instruction for novices. While some constructivists argue that "learning by doing" enhances learning, critics of this instructional strategy argue that little empirical evidence exists to support this statement given novice learners. Sweller and his colleagues argue that novices do not possess the underlying mental models, or "schemas" necessary for "learning by doing". Indeed, Mayer (2004) reviewed the literature and found that fifty years of empirical data do not support using the constructivist teaching technique of pure discovery; in those situations requiring discovery, he argues for the use of guided discovery instead.