This monograph presents a completely theoretical analysis of data pertaining to professional laboratory experiences at the preservice level. The intention is to bring together in a useful pattern what is known and what is asserted about these experiences and to make specific functional proposals that, if implemented, may be conducive to enhancing the quality of professional laboratory experiences. The publication is divided into discussions of the definition of professional laboratory experiences; their purpose; their role; the characteristics of high quality professional laboratory experiences; principles that should govern them; theory; educational concepts underlying them; types (directed observation, participation, and student teaching); range; facilities; and forward-looking developments. A bibliography is included. (JA)