Described is the evaluation of the pilot-test version of the Measurement of Length Unit , part of an instructional program developed by the Vocabulary Development Project, with 80 educable or trainable mentally handicapped primary grade children in either special classes within regular schools or in special schools. Feedback for the formative evaluation stage came from results of pretesting and posttesting, written evaluations of lessons by teachers, and classroom observations. Results are presented for each of the eight lessons in terms of objectives, performance of classes from neighborhood or special schools, and an interpretation. Summarized are comments from the teacher review board meeting. Results are discussed in terms of need for instruction, instructional effectiveness, design of the materials, content, sequencing, and test instruments. Results are seen to support the need for measurement instruction, with major changes being made in the sequencing of instruction and revision of the test. Appended are a description of the pilot-test version of the length unit, the pilot-test questions, a sample evaluation form, classroom observation forms, a description of the revised version of the measurement of length unit, and the revised length unit test. (DB)