This paper dealt with the use of classroom observation data for formative evaluation purposes, and with a research project in which scores based on observed performance of teachers in secondary school algebra and English classes were compared with efficiency scores based on an input-output model. The model, using Data Envelopment Analysis (DEA) and Constrained Facet Analysis (CFA), was developed by the Educational Productivity Council at the University of Texas at Austin. DEA/CFA was used previously to compare the outputs of schools or school districts that have similar inputs. This paper reported on the use of the model at the individual teacher level. An observation guide, developed from the process-product research, contained 39 indicators in 7 categories. Three trained observers visited 140 classrooms for a full period each visit. A comparison of the teachers' scores based on observed performance with their efficiency scores using the DEA/CFA input-output model revealed a high correlation for the algebra classes but no significant correlation for the English classes. (Author/JAZ)