Self-regulated learning (SRL), in which students monitor and adjust their learning, has been widely emphasized in education and school psychology. SRL is expected to be particularly crucial for students in correspondence high schools, where independent study constitutes the main part of learning. However, research on correspondence high school students' learning remains limited. This study examined how learning strategies, including SRL, relate to students' beliefs about learning and friendships and how these factors affect school adjustment and academic achievement. We also compared correspondence and full-time high school students. In total, 1,469 correspondence and 471 full-time high school students from the Tokyo metropolitan area participated in an online survey. They completed questionnaires on beliefs about learning and friendships, use of various learning strategies, and adjustment to school and peers. They also self-reported their academic achievement. Structural equation modeling revealed that learning beliefs influenced strategy use, which in turn affected academic achievement and school adjustment. Among correspondence students, autonomous learning beliefs strongly promoted strategies for self-reflection and improvement, behavioral regulation, and rehearsal. It was also found that beliefs favoring emotional and instrumental friendships enhanced peer adjustment directly and indirectly through the use of collaborative learning strategies. This indirect effect was particularly evident for instrumental friendship beliefs among correspondence students. These findings highlight the importance of self-regulated and collaborative learning for academic achievement and school adjustment. In correspondence high schools in particular, fostering autonomous learning beliefs, developing instrumental peer relationships, and providing opportunities for collaborative learning appear to be especially important for promoting effective learning and a fulfilling school experience.