This teacher's guide is for an elementary school science unit designed for use with third grade (or older) children in the schools of the Trust Territory of Micronesia. Although there is a degree of similarity to curriculum materials developed for the Science Curriculum Improvement Study, this Micronesian unit does not purport to be an adaptation or edition of the SCIS materials. Designed to be taught in the vernacular language, this unit was prepared to be a companion unit to one concerning populations, with the two units covering the school year. Activities are designed for active student involvement with the teacher acting as a guide. The unit involves the concepts of systems, variables, evaporation, temperature, and histogram and the science process skills of observing, communicating, predicting, inferring, and recording. The guide contains information concerning objectives, teacher and student activities, rationale for these activities, needed materials, teaching suggestions (provided on a day by day basis), and questions to be posed in class discussions. (PEB)