Computer-based testing (CBT) is becoming an increasingly popular format of assessment in educational settings. If students face a digital divide in terms of access to computers at school and at home, CBT may exacerbate measured student achievement gaps. In this paper, we use the rollout of CBT in South Carolina starting in 2015 to investigate its effect on measured student performance. We link student-level test scores and poverty measures to the share of students taking CBT in a grade of a school and show that CBT has a significant negative impact on test scores of multiple subjects. The negative impact is not uniform across student subgroups but rather particularly large for students in poor households. There is little evidence that the effect fades as students and schools become more experienced with computerized testing. These results suggest that the testing mode change might have distributional consequences. However, we do find a smaller effect in schools where technology is more readily available, implying that school-level investments could mitigate the effect.