This paper describes the general nature of a joint project between ETS and the New York City Board of Education to aid first grade teachers in observing, assessing and fostering the cognitive development of young children. Some of the materials developed for this project are also described and some of the educational measurement issues considered in developing these materials are briefly discussed. These issues include the teachers' need for continuous feedback; the need for evaluation devices that are easily comprehended by the teachers and less subject to misinterpretation; and the need for theoretically oriented tests. The materials developed include: 1) a teachers' guide to help them understand intellectual development and become better observers of children's cognitive development; 2) a set of written exercises in six areas of cognitive development; 3) a series of assessment tasks, and 4) instructional materials. The theoretical assumptions behind all these materials are briefly presented and discussed, and the teachers' guide is described in more detail. (The teachers' guide is divided into six broad areas--basic language skills, concepts of space and time, beginning logical concepts, beginning math concepts, the growth of reasoning skills, and general signs of development--each encompassing several concepts.