According to self-efficacy theorists, people's judgments of what they can accomplish are influential arbiters in human agency and, as such, powerful determinants of their behavior. In large part, this is because these self-efficacy beliefs are said to act as mediators between other acknowledged influences on behavior, such as skill, ability, previous accomplishments or subsequent performance. Path analysis was used to test the influence of writing self-efficacy, writing apprehension, perceived usefulness, and writing aptitude on the essay-writing performance of 218 fifth-grade students. A model that also included sex (gender) accounted for a 64% variance. Instruments were group administered in individual language arts classes during two periods. During the first period, students were asked to complete the self-efficacy, perceived usefulness, and apprehension instruments. During the second class period, students were asked to write the performance measure, a 30-minute essay. As hypothesized, self-efficacy beliefs made an independent contribution to the prediction of performance despite the expected powerful effect of writing aptitude. Aptitude also had a strong direct effect on self-efficacy. Self-efficacy had direct effects on apprehension and perceived usefulness. Girls and boys did not differ in performance, but girls reported higher writing self-efficacy, found writing more useful, and had lower apprehension. Results support the hypothesized role of self-efficacy in A. Bandura's social cognitive theory. (Contains 2 tables of data, a figure, and 43 references.) (Author/TB)