Metacognitive skills refers to individual abilities for regulating and controlling learning behavior. Orientation, goal setting, planning, monitoring, and evaluation are manifestations of those skills. Given that metacognitive skills directly affect learning behavior, they are a strong predictor of learning performance. Students display a huge variation in metacognitive skillfulness, dependent on age and experience. In this article, metacognitive skills are considered to be an acquired program of self-instructions, that is, an orderly series of condition-action rules that contain conditional knowledge about when to apply which skill, and operational instructions for how to implement a particular skill. This notion has implications for effective metacognitive instruction in deficient students. Prior to instruction, on-line assessments of metacognitive skillfulness during actual task performance are indispensable for the identification of deficient students and for tailoring metacognitive instruction to the individual needs of students. Instruction should subsequently address what skill to perform when, why, and how (WWW&H), embedded within the context of a given task. Moreover, instruction should explicitly inform students about the benefits of applying metacognitive skills to make them exert the required effort. Finally, teachers may act as role model to students by including explicit metacognitive instruction in their lessons.