This article explores three attributes of teachers' understanding of fraction magnitude: the accuracy and reasonableness of teachers' estimations in response to fraction arithmetic tasks as well as the alignment of the estimation strategies they used with the concept of fraction magnitude. The data were collected from a national sample of mathematics teachers in grades 3-7 in which fraction concepts were taught (N = 603). The results indicated the teachers' estimations were only partially accurate and reasonable, particularly when fraction division was involved. Furthermore, teachers' credentials and the grade level at which they taught mathematics were significantly related to teachers' understanding of fraction magnitude.

Attending to the whole unit that a number refers to in a mathematical problem situation and showing flexibility in coordinating different units are foundational for mathematical understanding. In this study, we explored teachers' attention to and flexibility with referent units in situations involving fractions and fraction multiplication. Using data collected across the USA from 246 mathematics teachers in Grades 3-7 where fractions are taught, we found that teachers' attention to and flexibility with referent units were related to each other as well as to teachers' overall knowledge of fractions.

In this paper, we focus on the design of assessments of mathematics teachers' knowledge by emphasising the importance of identifying the purpose for the assessment, defining the specific construct to be measured, and considering the affordances of particular psychometric models on the development of assessments as well as how they are able to communicate learning or understanding. We add to the literature by providing illustrations of the interactions among these critical considerations in determining what inferences can be drawn from an assessment. We illustrate how the considerations shape assessments by discussing both existing and ongoing research projects. We feature discussion of two projects on which the authors of this paper are collaborating to demonstrate the affordances of attending to all three considerations in designing assessments of mathematics teachers' knowledge to provide readers with opportunities to see those considerations in use.