The Discovery-Expository Instrument is a classroom observation scale which measures the position of a teacher's presentation on a continuum of discovery presentation (in which the student is encouraged to solve problems with minimal help from the teacher), to expository presentation (in which the teacher provides a complete description and discussion of the subject). Teachers are rated on categories of behavior including: (1) definitive; (2) explanative; (3) clarifying; (4) exemplative; (5) summarizing; (6) question-raising; (7) problem-structuring; (8) directive-managing; and (9) neutral. Sixteen signs are also used to rate discovery versus expository teaching behavior. Four studies involving different grade levels were conducted which suggest that the instrument possesses relatively high inter-observer and intra-observer reliabilities and high validity. Using this instrument can help a researcher assess and, consequently, control the independent variable of level of discovery presentation in the classroom and the laboratory. The instrument also can be used to monitor the actual implementation of curriculum materials by the teacher, such as by gauging the nature and consistency of a teacher's use of new materials. An abbreviated version of the instrument; scoring directions; and the 16 signs and nine category descriptions are appended. (Author/GDC)