The aim for this article is to generate theory on activity that many teachers perform; the practice of improvisation. Improvisation is a professional method in teaching practice that very often is so taken-for-granted that it to some extent is under-theorized in the area of educational research. In education, an important purpose of the robustness of research involves educational practice. And so, the article is based on arts-based co-teaching project experiences. A primary school teacher and I set the project in a basic education public school in Vaasa, Finland in school year 2015-2016. Improvisation is here approached from a position formed by participatory research practice. Co-mentoring theory (Cf. Mullen, 2012) serves as a backdrop for understanding how the article creates a relation between co-teaching experiences and theory-based reasoning on the phenomena. The research method is informed by a/r/tography. The research question is: what are the elements that can be recognised as improvisation in the teaching experiences from the project? In the project the following questions related to improvisation and development of teachers’ professional work were articulated: What are the elements of meanings and interests in teaching improvisation practice? How can we better understand the didactic character of improvisation in teaching practice? What are the outcomes for the profession? How do the connections between art and pedagogy practice show when approaching the practice in order to promote curriculum and instruction development in improvisation as teaching practice?