“…The practice-based CKT assessments that measure the knowledge used in teaching science focus mainly on science teachers' pedagogical content knowledge (Lee, Brown, Luft, & Roehrig, 2007) and involve teachers in tasks that require substantial time to administer and score, such as analyzing video-recorded episodes of practice (Roth et al, 2011), participating in think-aloud or cognitive interviews (Henze & van Driel, 2015;Park & Suh, 2015), conducting classroom observations (Park & Oliver, 2008;Park & Suh, 2015), or documenting their pedagogical content knowledge for particular science topics using graphic organizers (Bertram & Loughran, 2012;Loughran, Mulhall, & Berry, 2004). To date, only a few notable efforts have developed large-scale, practice-based assessment items to measure the professional knowledge specialized to science teaching (Sadler, Sonnert, Coyle, Cook-Smith, & Miller, 2013;Smith & Taylor, 2010).We think that this tasks of teaching framework offers a more focused conceptualization of the measurable aspects of the CKT science construct, which addresses some of the concerns in the field about the need for increased clarity regarding the nature of CKT science and what is being measured (Abell, 2008;Gess-Newsome, 1999;van Driel, Verloop, & de Vos, 1998). In our work, we focus on the conceptual challenges that elementary science teachers encounter in the work of teaching science and on developing practice-based assessment items to measure the CKT that is embedded within these recurrent tasks of teaching.…”