An angles teaching sequence was designed, in which students were guided to abstract a general concept from physical activities with concrete materials. The three design principles used were familiarity, similarity recognition, and reification. The resulting teaching sequence was tested in a field study involving 25 teachers of Grades 3-4. The data collected demonstrate the significance of the three design principles, and the results from pre- and post-assessment interviews provide evidence for the overall effectiveness of the lesson sequence. Also earlier findings that angle is a multifaceted concept which is difficult to learn are supported. (Contains 3 figures.) [For complete proceedings, see ED500860.]