Teaching one thing at a time or several things together? – teachers changing their way of handling the object of learning by being engaged in a theory-based professional learning community in mathematics and science

Twelve lower secondary schoolteachers in mathematics and science were asked to teach a topic of their choice during a lesson that was video-recorded. We were able to analyse 10 of the cases and we found that all of them were similar in one respect: concepts and principles were introduced one at a time, each one followed by examples of the concept or principle in question, apparently to highlight its essential meaning. All the teachers...