The document describes a practicum which developed a unit on critical thinking that applied Jerome Bruner's discovery-learning method and also incorporated the unit within the curricular requirements of elementary education majors at Castleton State College in Vermont. It is presented in five sections and an appendix. Section I provides introductory material, including the rationale. Section II explains the background and significance of the practicum, exploring the critical thinking theories of David Wright, Benjamin Bloom, Hilda Taba, Jerome Bruner, and J. Richard Suchman. Section III defines discovery/inquiry learning as finding "the regularities of previously unrecognized relations and similarities between ideas with a resulting sense of self-confidence in one's abilities." Reasoning competencies/critical thinking skills are defined as "processes inclusive of, but not limited to problem solving, classification and organization, making reasoned judgments, and logic." Procedures used in developing the miniunit are explained. Section IV lists the results of the practicum, including development of the unit, an increase in students' knowledge of reasoning competencies, and the unit's inclusion in a required education course. Section V examines implications and recommends further research and modifications. The appendix presents the unit, including rationale and objectives, a list of 15 basic reasoning competencies, and 27 possible teaching activities related to each competency. Activities include reports, class visits, map work, classification activities, and dilemma solution. (CK)