Teachers rely on mental planning throughout the design, implementation, and evaluation phases of instruction. This paper focuses on the elementary school teacher's use of instructional design (ID) skills in the planning and delivery of instruction, emphasizing the relative and "real" use of ID practices in both mental and written planning. Two studies of elementary school teachers, one involving 22 teachers from schools across North Carolina, the other involving 17 teachers from Provo School District in Utah, addressed planning issues and practices by yearly, unit, and daily planning. Results of both studies, illustrated in 12 data tables, indicated: (1) teachers favored mental planning; (2) plans were more specific at the unit and daily levels; (3) most teachers with formal training in ID felt it had improved their planning processes; (4) most teachers consciously used ID processes in planning; (5) the crucial elements of the ID process were goals, learner analysis, objectives, activities and strategies, tests, and revision; (6) ID processes received more attention at the unit and daily levels; (7) most teachers gave equal importance to written and mental planning; (8) during teaching there was less deviation from unit and daily plans than from yearly plans; (9) initial planning decisions centered around content and objectives, while most planning time was spent on content, materials, and activities; and (10) testing instruction prior to using it in the classroom was impractical. Ways for teachers and instructional designers to work together include: (1) developing a common technical language of instruction; (2) validating the scientific bases of teaching as essential precursors of the art of teaching; (3) adopting a layers-of-necessity philosophy in modifying classical ID to meet the needs and practices of teachers; and (4) recognizing the need for gradual reform and fundamental systemic restructuring as concurrent, interactive ventures. (Contains 37 references.) (Author/SWC)