The study investigates the effects of bilingualism and biliteracy on thought organisation, and syntactic complexity in the written production in a group of fifty 11-year-old children (M = 10.7) enrolled in 5th and 6th grades in a bilingual school in the south of Brazil. The children’s home and community language is Portuguese, and they have been exposed to English at school for 10 hours a week for at least five years. Participants were asked to create a narrative based on a sequence of five images (Cambridge Assessment, 2018), being one in English and one in Portuguese, in a counterbalanced order. Thought organisation (connectivity) was measured through the analysis of graph trajectories performed with the computational tool Speech Graphs (Mota et al., 2014, 2016, 2019) and the analysis of syntactic complexity involved the assessment of T-Units (Hunt, 1965). Results indicated a moderate positive correlation in the attributes of thought connectivity and the levels of syntactic complexity in both languages, demonstrating that, as children advance in the development of more complex writing strategies in Portuguese, they progress in their written production in English to the same extent.