During the COVID-19-related school closures teachers and students were challenged to suddenly switch to digital teaching at a distance. In particular, the challenge was to organize high-quality teaching in which students stay on task. Familiarity with technology may have helped to master the situation. However, only few studies so far have examined the quality of digital distance teaching (e.g., cognitive activation) during school closures and its relation to students' learning (e.g., effort investment). Moreover, systematic research concerning the role of familiarity with technology-enhanced teaching and learning acquired during face-to-face teaching is yet lacking. In our study, we used data from 729 ninth graders to investigate how student-observed learning activities when using technology at a distance were related to students' effort in learning in two subjects (mathematics, German). In addition, we examined whether student-perceived cognitive activation mediated this relation. Finally, the sample provides the unique opportunity to examine the role of familiarity, as some of the classes had been randomly equipped with tablet computers one year before the school closures and thus had the opportunity to gain familiarity with using technology in the classroom. Results from structural equation models showed that student-observed learning activities were associated with students’ learning effort in both subjects. Student-perceived cognitive activation mediated this association. Familiarity with face-to-face technology-enhanced teaching gained before the COVID-19 pandemic appeared to be less important for high-quality digital distance teaching. Thus, infrastructural measures, such as equipping schools with digital devices so that teachers and students can familiarize themselves with technology, do not seem to be decisive for high-quality digital (distance) teaching—at least in the case of short-term change from face-to-face to digital distance teaching, as was necessary during the COVID-19 pandemic.