Prior studies have not tested whether an instructional intervention aimed at improving metacognitive skills results in changes to student metacognition, motivation, learning, and future learning in the classroom. We examined whether a 6-hr intervention designed to teach the declarative and procedural components of planning, monitoring, and evaluation could increase students' metacognition, motivation, learning, and preparation for future learning for middle school science. Forty-six eighth-grade students were randomly assigned to either a control group, which received extensive problem-solving practice, or an experimental group, which received more limited problem-solving practice along with metacognitive instruction and training. Results revealed that those who received the metacognitive instruction and training were less biased when making metacognitive judgments, p = 0.03, d = 0.65, endorsed higher levels of motivation after instruction (e.g., there was a large effect on task value, p = 0.006, d = 0.87), performed better on a conceptual physics test, p = 0.03, d = 0.64, and performed better on a novel self-guided learning activity, p = 0.007, d = 0.87. This study demonstrates that metacognitive instruction can lead to better self-regulated learning outcomes during adolescence, a period in which students' academic achievement and motivation often decline.