Reading comprehension is essential for students' ability to build knowledge. Students' comprehension abilities can be enhanced by providing students with deliberate practice and formative feedback on reading comprehension strategies. iSTART is an Intelligent Tutoring System (ITS) that is designed to provide instruction in reading strategies with minimal teacher supervision -- affording the ability to teach reading strategies at scale. In the current study, undergraduate students received reading strategy instruction and opportunities for deliberate practice via the iSTART intelligent tutoring system or not (i.e., no-treatment control group). Participants' reading comprehension and psychology knowledge were assessed. The iSTART group demonstrated substantially greater scores than the control group on a post-training reading comprehension measure (Cohen's d > 1.0). The average psychology knowledge scores did not differ between iSTART (post-training) and control groups, but overall these scores were unexpectedly low. Within the iSTART group, there was no difference in reading comprehension and knowledge scores as a function of students' different behaviors in the system. Overall, the results indicate that iSTART is an effective tool to teach reading strategies at large scale. However, further work is required to test the extent to which iSTART supports knowledge building. [This paper was published in: "Proceedings of Learning @ Scale conference (L@S '24)," ACM, 2024.]