The paper focuses on the analysis of the effectiveness of virtual co-teaching. Virtual co-teaching is an emerging form of learning that uses the physical presence of one educator and the virtual presence of another. Thus, it allows teachers or experts who cannot be physically present for various reasons to join the teaching process. This specific form of teaching is being developed within a project supported by the Technology Agency of the Czech Republic at the Faculty of Education of Charles University. However, for its wide use it is necessary to verify the effectiveness of the virtual form of co-teaching, to identify and describe its possibilities, but also its obstacles and limitations, which is the aim of the present paper.
Currently, the literature describes five to nine different types of co-teaching classes, depending on the distribution of activities among individual teachers, the division of roles and responsibilities of both educators. The basic types of co-teaching include the so-called tandem teaching, where both educators are equal, and the model where one educator teaches and the other supports (for details see Beninghof, 2012, Murawski, 2017, Dove et al., 2018, Veteška et al., 2020, Kursch, 2021).
In the pre-research phase, we conducted a scoping review in 2020, looking at the topic of co-teaching effectiveness and the factors that influence it. Based on the 19 research studies analyzed, we identified core categories that influence the flow of co-teaching sessions. These were mainly the definition of the roles of individual educators and their relationships with each other, the time devoted to preparation and the overall setup of teacher collaboration. Of course, the composition of the learners also contributed to the effectiveness of the lessons, where special attention was paid to studies describing co-teaching in the context of special educational needs. Virtual co-teaching was the subject of only 5 of the analysed studies, in which the technical side of things was repeatedly mentioned as a key prerequisite for quality education. Without a mastered and well prepared technical support, it was not possible (regardless of the relationships and quality of educators) to provide an effective virtual teaching unit (Veteška et al., 2020). The importance of sharing and involving different actors in the educational process is also a current topic at the level of educational policy, both national Czech and European. As the text of Strategy 2030+ states "Sharing examples of good practice is proving to be one of the most effective methods of improving the quality of the education system, and it is imperative to apply it both across levels of education management and among teachers themselves." (Fryč et al., 2019 p. 62). Thus, addressing collaboration and sharing of the pedagogical process among educators is an important task of contemporary pedagogy. The combination of co-teaching with a virtual component then accentuates, in addition to the mentioned collaboration, the current demand for digitalization and the overall need to respond to the current changes in society (see also Veteška and Kursch, 2019).

In order to achieve the research objective, i.e. to determine whether virtual co-teaching is equally effective in meeting the lesson objectives and to describe its possibilities, advantages, obstacles and limitations, we chose a case study design. This is a qualitative methodological approach that analyses and describes in detail aspects of the case under study, which is virtual co-teaching in the classroom. The case study design is characterized by a detailed analysis and description of the case through in-depth and multi-source information gathering (Hendl, 2016, Švaříček and Šeďová, 2014), which is key to truly understanding the phenomena under study in their natural context. In line with the case study approaches, we used both quantitative and qualitative methodological approaches to describe the case under study in detail. However, the qualitative part was the core part, relying on individual and group semi-structured interviews (2 individual and 2 group interviews were conducted in total), document analysis and structured classroom observations (2 observations were conducted). The results of the implemented lessons projected the students' knowledge and were then verified in accordance with the whole experiment by means of a knowledge test.

Our findings suggest that co-teaching could be a full-fledged alternative to traditional co-teaching in terms of the impact on learning represented by ex-post test scores. However, in terms of effectiveness, other non-numerical factors that affect effectiveness must be accepted. These factors are based on the experiences and opinions of teachers and pupils and the limitations imposed by the human factor. However, if we look at effectiveness in terms of outcomes and costs, it is necessary to accept that virtual co-teaching appears to be more effective than traditional co-teaching because of the savings in travel costs and the availability of educators and experts.

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