The benefits of rich tasks, project-based learning, and other inquirybased approaches in terms of student understanding and engagement with mathematics are well documented (e.g., Fielding-Wells, Dole & Makar, 2014; Lam, Cheng & Ma, 2009; Sullivan & Lilburn, 2004). Such pedagogies are consistent with the development of mathematical proficiencies as described in the Australian Curriculum: Mathematics (Australian Curriculum Assessment and Reporting Authority [ACARA], 2013) and many teachers are keen to implement them. Basing mathematics teaching around projects and ill-structured problems, however, can be daunting for teachers who lack confidence in the mathematics content that they are teaching. In addition, Toolin (2004) reported concern among teachers and parents that students in schools using project-based learning might not have access to the whole curriculum. This paper describes an investigation of the relationship between the length of a pendulum and its period (time for one complete swing) conducted as part of a professional learning program with ten teachers in a Year 9–12 school attempting to teach the entire curriculum using project-based learning 1 . As described by Beswick, Callingham and Muir (2012) none of teachers at the school had studied mathematics beyond secondary school. Nevertheless, they were reasonably adept at identifying at least some of the mathematics that could be taught using a particular context although they struggled to know how to engage students with the mathematics (Beswick et al., 2012). They were also concerned about whether it would be possible to cover the entire mathematics curriculum using only projects. The pendulum investigation was intended to illustrate the extent of the mathematics that could potentially be taught through a single investigation and to build teachers’ confidence in exploring mathematics with their students. Content from the Australian Curriculum: Mathematics that was ultimately touched upon is shown in Table 1. The investigation