In comparing lesson 1 with lesson 2 it was evident how all four teachers’ intentions
became more clearly expressed and the content more limited in the second lesson
compared to the first (e.g. Kay’s way of focusing acid and bases as two opposite characteristics).
As a consequence, the intended object of learning was more in line with the
enacted object of learning. In lesson 2, connecting the diode correctly and recognizing
the differences and connections between acids and bases, atoms and ions and force
and pressure were focused. As such, a key insight for all teachers was to limit the learning
object, and thus discern the science ‘Big Idea’ (Loughran et al., 2006; Nilsson &
Loughran, 2012), and develop an increased knowledge about the relationship between
subject content, teaching and student learning, in other words, those aspects that are
central to a teachers’ PCK. The teachers’ ways of identifying and focusing on that
which was to be learnt also refers to the PCK component knowledge of science curriculum
described by Park and Oliver (2008) as a knowledge that ‘enables teachers to
2852 P. Nilsson and A. Vikström
identify core concepts, modify activities, and eliminate aspects judged to be peripheral
to the targeted conceptual understandings’ (p. 266).