Most research on the flipped classroom employs group-based interactive learning activities inside the classroom, citing student-centered learning theories based on the works of Piaget (1967) and Vygotsky(1978). The exact nature of these activities varies widely between studies. Similarly, there is wide variation in what is being assigned as "homework". The flipped classroom label is most
often assigned to courses that use activities made up of asynchronous web-based video lectures and closed-ended problems or quizzes. This implies that technology is central to the success of this approach