In order to determine whether the use of two types of teacher written responses to student essays--clarifying and directive--produced significant differences in writing performance growth, 28 12th grade students in a metropolitan Nebraska high school were randomly divided into two groups. Each group received one of the two types of teacher response for eight essays during the experimental period, while three pretest and posttest essays rated by a team of independent raters provided entering and ending measures of quality in student writing performance. Student t-tests were computed for 42 comparisons of interest for three hypotheses. The .05 level of confidence comprised the significant criterion. Findings led to the conclusions that neither type of teacher response (1) assured general, mechanical, or total writing performance growth during an academic semester, (2) consistently influenced growth in writing performance between contiguous units of study, or (3) consistently influenced growth on revisions. In the last two categories, clarifying responses did show slight advantages in specific instances. (Author/JM)