Metasyntactic Ability (MSA) refers to the conscious reflection about syntactic aspects of language and the deliberate control of these aspects (Gombert, 1992). It appears from previous studies that heritage-language learners tend to demonstrate lower MSA than their monolingual counterparts (Lesaux & Siegel, 2003). In the present study, we verified whether the same results would be obtained among Portuguese heritage children living in a French-speaking environment when their MSA is measured using two different tasks. The participants were 22 Portuguese heritage children and 22 French monolingual elementary school children (mean age = 10.9 years). Five measurement instruments were used: a reading comprehension task; a language proficiency task; two metasyntactic tasks: a replication task in which the children had to identify and reproduce an error, and a repetition task, in which they had to repeat sentences containing syntactic errors; and a sociodemographic questionnaire. The results showed that when reading comprehension and language proficiency were controlled for, no effect of language background could be observed. However, reading comprehension and language proficiency differently influenced performances on MSA tasks.