The Smarties-Box Challenge encourages students to apply several different mathematical capabilities and concepts--such as, estimation, multiplication, and the notion of being systematic--to solve a complex, multistep problem. To effectively engage in the Smarties-Box Challenge, students are required to demonstrate aspects of all four proficiency strands identified in the "Australian Curriculum: Mathematics"--problem solving, understanding, reasoning and fluency. The Smarties-Box Challenge requires students to employ a diverse range of mathematical skills and capabilities, as they work together as a team to solve quite a complex estimation problem. Undertaking the Smarties-Box Challenge is also great fun and tends to engage the whole-class (not least because of the Smarties "dangling" as a prize at the end). It is a highly worthwhile activity for primary school students in Year 3 onwards.