Path analysis was used to test the influence of writing self-efficacy, self-concept, apprehension, and aptitude on the essay-writing performance of 181 ninth-grade students in a public high school in the southwestern United States. A model that also included gender accounted for 53% of the variance in performance. As hypothesized, both aptitude and students' own confidence had strong direct effects on performance. Aptitude also had a strong direct effect on self-efficacy, which largely mediated the indirect effect of aptitude on performance. Self-efficacy had a strong direct effect on apprehension, which, in turn, had a weak direct effect on performance. Although girls and boys did not differ in aptitude or performance, girls expressed less confidence in their writing. Additionally, Hispanic students had lower performance scores as well as lower levels of confidence and self-concept and higher apprehension. Results support the hypothesized role of self-efficacy in A. Bandura's (1986) social cognitive theory. (Contains 47 references, 4 tables, and 1 figure of data.) (Author/RS)