This study aimed at examining: (a) students' metacognitive knowledge and metacognitive regulation when they are doing school work or homework, and their self-regulated learning style regarding the four different types of behavioral regulation: external, introjected, identified and intrinsic; and (b) the role of metacognition in self-regulated learning style, and in the impact of self-regulated learning style on performance expectations, and subsequent performance in the school subjects of language, mathematics and physical education. The sample comprised of 243 primary school students, fifth and sixth grades, boys and girls, who randomly came from 20 state primary schools of various regions of Greece. The participants completed the scales at the middle of a school year, while their school performance was estimated by the teachers. The results showed that: (a) the students used metacognitive knowledge (predominately, declarative) and metacognitive regulation (mainly, planning) at a moderate extent, and they reported a mixed profile of self-regulatory learning style, favoring identified; (b) metacognitive regulation, compared with metacognitive knowledge, was a more powerful formulator of regulatory learning styles, mainly intrinsic and identified; (c) metacognition explained a small percentage of variance of both performance expectations, beyond self-regulatory style, and performance, beyond the interactive effect of performance expectations and regulatory learning style, in both language and mathematics, while it had no significant unique contribution in physical education; (d) external regulation had negative contribution in school performance across the three school subjects, while intrinsic regulation