Globally, the disruptions to higher education caused by COVID-19 required most campuses to make impromptu shifts to emergency remote teaching (ERT). When compared to traditional online education, ERT generally falls short in terms of pedagogies, pacing, and/or successful modality implementation. Elsewhere, it is established that the sudden shift towards online and asynchronous ERT delivery creates student challenges, especially in terms of internet unavailability and social disconnectedness. What remains understudied is the impact of COVID-19 on actual student learning. We address this knowledge gap using a natural research design where we (i) evaluated sustainability learning for traditional in-seat and online human geography students in Fall 2018 and (ii) obtained federal funding to evaluate sustainability learning for ERT and online students in Spring 2020. Results from the analysis indicate that in-seat students outperformed online students prior to COVID-19 on a standardized sustainability knowledge assessment by 13%. Results also indicate that in-seat students prior to COVID-19 (Fall 2018) outperformed ERT students (Spring 2020) by 28%. Discussion and limitations are provided.