Knowledge, although seemingly available, is often not used for problem solving. That means it remains "inert." Three types of explanations exist for this phenomenon. Metaprocess explanations assume that the relevant knowledge is available, but it is not used because of disturbed access processes (e.g., lacking metacognitive control). Structure deficit explanations suppose that the deficit is rooted in the structure of the knowledge itself (i.e., the knowledge is not available in a form that allows for its application). In situatedness explanations, the traditional concepts of knowledge and transfer are questioned. One basic assumption of this perspective is that knowledge is fundamentally situated (i.e., context-bound). In the last decade, instructional models have been developed that try to remedy the inert knowledge problem and take into account important aspects that have been raised by the different explanations.

In this paper, we critically analyze how the concept of negative knowledge contributes to the understanding of professionals’ expert practice and learning. Negative knowledge is experientially acquired knowledge about what is wrong and what is to be avoided during performance in a given work situation. In terms of its theoretical foundation, the concept relates to constructivist theorization and metacognition. Building on existing conceptions of negative knowledge, we systematically relate the concept to research on expertise and learning from errors. The concept of negative knowledge augments existing theories of professional knowledge by emphasizing knowing about what to avoid as part of experts’ effective actions. During routine actions, negative knowledge enhances professionals’ certainty of how to proceed and increases the efficacy through the avoidance of impasses and suboptimal problem-solving strategies. Quality and depth of reflective processes after actions are related to the development of negative knowledge. The potential of negative knowledge for the investigation of professional learning is discussed through reference to recent empirical work.

Classrooms full of pupils can be very overwhelming, both for teachers and students, as well as for their joint interactions. It is thus crucial that both can distil the relevant information in this complex scenario and interpret it appropriately. This distilling and interpreting happen to a large extent via visual perception, which is the core focus of the current Special Issue. Six empirical studies present examples of how to capture visual perception in the complexity of a classroom lesson. These examples open up new avenues that go beyond studying perception in restricted and artificial laboratory scenarios: some using video recordings from authentic lessons to others studying actual classrooms. This movement towards more realistic scenarios allows to study the visual perception in classrooms from new perspectives, namely that of the teachers, the learners, and their interactions. This in turn enables to shed novel light onto well-established theoretical concepts, namely students’ engagement during actual lessons, teachers’ professional vision while teaching, and establishment of joint attention between teachers and students in a lesson. Additionally, one theoretical contribution provides the very first model of teachers’ cognitions during teaching in relation to their visual perception, which in turn will allow future research to move beyond explorations towards hypothesis testing. However, to fully thrive, this field of research has to address two crucial challenges: (i) the heterogeneity of its methodological approaches (e.g., varying age groups, subjects taught, lesson formats) and (ii) the recording and processing of personal data of many people (often minors). Hence, these new approaches bear not only new chances for insights but also new responsibilities for the researchers.