The focus of this paper is how the open micro blog service Twitter can be used as backchannel in a formal educational setting and what impact it might have on teaching when used by the students.

Yngve (1970) was the first researcher to use the concept backchannel. In short, he specified backchannel to be the part of a conversation where the person who has the turn understands that the person listening also is involved by giving response in different ways by, for example, humming and nodding. Like Atkinson (2010), we claim that backchannel is "a line of communication created by people in an audience to connect with others inside or outside of the room, with or without the knowledge of the speaker at the front of the room" (p 17).

The aim of this paper is to describe from a teacher’s perspective how a backchannel conversation using Twitter affected the teaching. The following five aspects are highlighted:

Synchronous:

1. Communicative significance of backchannel in the teaching situation.
2. Importance for teaching and how it affects the teacher in the classroom situation.

Synchronous and asynchronous:

1. Backchannel as synchronous and asynchronous evaluation tool, both in terms of activity, teaching materials and the teacher’s own performance.

Asynchronous:

1. Communicative significance of backchannel after the teaching situation.
2. Backchannel as tool for assessment purposes, primarily in relation to student achievement.

Learning as a result of "participation" in a social context is a core element in many of our most influential learning theories (e.g. Lave & Wenger, 1991; Vygotsky, 1978; Wenger, 1998). Wenger claims that learning is a complex process that combines activities such as talking, thinking, feeling, doing and belonging. Learning is primarily a social process and this motivates emphasizing participation and collaboration in the learning situation.

Teaching in schools means a community system including rules to be followed. The division of work reflects the different roles that individuals have in the system (Bellamy, 1996). Such activity system encounters contradictions that require some form of qualitative change. When an activity system undergoes a change, it creates a new practice, which was not there from the beginning (Engeström, 1996). Engeström (1987) describes this dynamic phase of the activity theory as "learning by expanding". In an activity system, contradictions occur­ periodically. New qualitative stages arise after re-organization as solutions to the contradictions. On the basis that human activity has its roots in human needs, contradictions and object orientation; activity theory explains how new knowledge can be developed. This contradiction is, and it can be formulated as a social dilemma, which can only be solved by collective actions from which new forms of activity occur. The new activity undergoes three stages: the state of needs, the state of motivation and the change of needs and activity.

The impact of new technology in teaching will be determined as much by the individuals mediating their objectives through technology as by the existing tools and the present community structure (Bellamy, 1996).

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