This is one of a series of units for environmental education developed by the Highline Public Schools. This unit, designed for third- and fourth-grade students, emphasizes cycles and focuses on the water, oxygen, and nutrient cycles. The eleven lessons in this unit are designed to take one-half to one hour each. Use of the extra activities would increase the time for most lessons. Each lesson includes the concept of the lesson, materials needed, notes to the teacher, procedure, evaluative activities, and suggested additional activities. The materials were tried and evaluated; evaluation data may be obtained from the Highline Public Schools. (RH)