This study investigated the effects of different versions of Web-based instruction focused on text structure on fifth- and seventh-grade students' reading comprehension. Stratified random assignment was employed in a two-factor experiment embedded within a pretest and multiple posttests design (immediate and four-month delayed posttests). The two factors were type of feedback provided by the Web-based tutor (elaborated vs. simple feedback) and the motivational factor of choice of text topics in practice lessons (student choice of texts vs. no choice). These factors were examined to learn how they affected performance after the six-month, 90-minutes/week intervention. Students who received elaborated feedback performed better on a standardized test of reading comprehension than students who received simple feedback. Learning how to attend to errors from the elaborated feedback tutor yielded large gains in test performance. Simple feedback did not help the least skilled third of readers move from complete lack of competency to competency using the structure strategy with problem-and-solution text. Choice between two topics for practice lessons did not increase reading comprehension. Substantial effects sizes were found from pretest to posttest on various measures of reading comprehension: recall, strategy competence, and standardized reading comprehension test scores. Maintenance of performance over summer break was found for most measures. The study informs research and teaching about Web-based reading tutors, feedback, comprehension, and top-level text structure. (Contains 16 tables, 8 figures and 2 notes.)