Basic advice for writing computer dialogs for use in science instruction is given. At the outset one should decide where within the subject area the computer dialog could offer a unique advantage over conventional teaching tools. Examples of such effective uses are remedial programs, in which a computer dialog may rapidly determine a student's particular weaknesses, and the interactive proof, where the student is allowed to demonstrate motivation and originality. In program writing, the model of human dialog is an effective tool. The goals, the style and the structure of student-computer dialogs are discussed, with samples of good dialog usage included in the appendix. (RB)