Results of a study conducted to develop and validate an instrument for objective and continuous assessment of student performance in the physics laboratory are reported. Two modes of teacher assessment of student performance were compared: (1) video-tape recording of two students performing experiments; and (2) an instrument for continuous, objective assessment of student performance. Results include findings that teachers using the instrument considered all student skills and that greater uniformity in assessment was achieved. An attitude assessment revealed that teachers demonstrated a high positive attitude toward use of the instrument. (Author/CS)