Making decisions, reasoning, and constructing arguments with scientific evidence are essential skills for all members of society, especially in a world facing complex socioscientific issues such as climate change and pandemics. Argumentation is a complex linguistic practice but little is known about how students from diverse language backgrounds engage in argumentation. The goal of this study was to identify how students' English language proficiency and history was associated with the reasoning demonstrated in their written arguments. We found that students with lower English proficiency and less English history produced fewer causal responses compared to students with higher English language proficiency and history. Follow-up interviews with fifteen participants revealed that students' comfort communicating in English on assessments was affected by a combination of general and academic language experiences. Findings suggest a need to identify the barriers encountered by students from diverse language backgrounds during argumentation to ensure students from all language backgrounds have equitable supports and opportunities to demonstrate their scientific abilities.