This paper examines intersections between mathematical and language performance in light of data collected from Hispanic students at varying stages of acquiring English as a second language at school. Emphasis is on aspects of the developing linguistic system as it affects underlying metacognitive processes related to mathematical performance. Sections of the report consider metacognition and bilingual learners; cognitive/academic language proficiency (CAL) and cognitive, analytic, mathematical proficiency (CAMP) intersections; the language of mathematics and metacognition; and the learning of mathematics in terms of person, task, strategy, and the regulation of cognition. Finally, implications for mathematics education are presented. Illustrations of behaviors of learners from primary grades to adults are interspersed. (MNS)