The hidden or overlooked nature of many of educators' professional activities complicates the already difficult task of supporting educators' labour--in both K-12 and higher education settings. These efforts can be understood as types of "invisible labour." Following PRISMA standards, we conducted a systematic literature review to answer a single research question: "How have scholars framed educators' professional activities in terms of invisible labour?" This systematic review searched 10 educational databases and identified 16 peer-reviewed journal articles spanning 2011-2021. From thematic analysis of these studies, we developed a model of five types of invisibility that intersect and mask educators' professional efforts: background, care, precarious, identity and remote labour. The review also showed several overall themes related to educators' invisible labour, which we discuss in connection to the literature: effort is often semivisible, invisibility is subjective, effort by marginalised educators is often overlooked, labour in unexpected places often means effort is overlooked, and there are layers of factors masking effort. We then discuss implications for practice, starting with five invisible labour questions to prompt reflection, then how to apply invisible labour as an improvement lens for identifying needs, allocating resources, analysing jobs and tasks, and evaluating performance.