The approach to computer-based instruction for third and fourth grade elementary students which is sketched teaches component placement, capitalization, and punctuation skills of addressing envelopes within the context of a simulated envelope. Part of a larger design for a complete program of composition instruction, this program comprises a set of materials for use on a microcomputer which can be used as a discrete unit of instruction. The skills taught are identified, i.e., placing the address and return address in the correct space on an envelope; capitalizing persons' names; capitalizing personal titles; capitalizing the names of streets, cities, and states; and using a comma to separate city and state. Then, the orientation procedures students undertake after they have loaded the program disk are discussed, the mainline instruction and practice is outlined, and the corresponding branching that occurs in response to students' performance on the tasks is described. The reporting system that provides information for teachers on the progress of all students using the program is also explained. (Author/LMM)