This 20 page document is the first in a series on how to write an expository essay at the primary level, (especially for second and third grade students.) This document is a complete module for a four day unit on writing a topic sentence, that includes objectives, pacing, lessons, a survey, teaching tools, writing samples, activities for students, homework, assessments and grading rubrics for evaluating a topic sentence. Instruction is explicit and assessment is easily measureable.