In this qualitative, descriptive case study, we examine how elementary emergent bilinguals (EBs) use disciplinary language as they engage in integrated science and engineering instruction. Instruction incorporated language and developmental scaffolds corresponding to EBs' language and content learning needs. Oral production of EB kindergarten to second-grade triads was analyzed to assess disciplinary literacy relevant to science inquiry and the engineering design process (EDP). Results demonstrate EBs' use of disciplinary language shifted from paraphrasing ideas to "build on" others' ideas and to challenge ideas or reason about evidence in ways that approximated science and engineering disciplinary communication norms. The scaffolds incorporated into the integrated science and engineering units allowed early EBs to successfully engage in disciplinary discourse practices leveraging their full semiotic resources. These results indicate young EBs can reason about evidence and engineering design constraints when provided instructional activities and scaffolds designed to address their language and developmental needs.