knowledge creators and engagement

I am interested in how knowledge building communities can enhance engagement (social and cognitive). But the question is how do you measure engagement? A recent literature review has prompted more questions that answers.

What does engagement look like?
Is it the number of times that students contribute to the discussion? The depth of the contribution? The amount of times an idea is revisited and revised? Or is it something altogether more holistic, such as a reflective thinking portfolio? (Lee, Chan and Aalst, 2006)

Knowledge building teachers, if we think knowledge building enhances engagement in classes, how can identify it.
I would love to hear your ideas and experiences.

Defining Engagement - Collaborative task WHS

Defining Engagement

Engagement is a complex and broad concept. There are visible elements (what we can see within the four walls of our classroom), and invisible elements(the emotional and the cognitive).  What influences engagement within a classroom though? How do you shift what is valued, or how a subject is percieved?