There are also scholars who have proposed thatthose tasks should be appropriately challenging. Christiansen and Walther
(1986), for example, argued that non-routine tasks, because they build connections between different aspects of learning,
provide optimal conditions for thinking in which new knowledge is constructed and earlier knowledge is activated. Similarly,
Kilpatrick, Swafford, and Findell (2001) suggested that teachers who seek to engage students in developing adaptive
reasoning and strategic competence, or problem solving, should provide them with tasks that are designed to foster those
actions. Such tasks clearly need to be challenging and the solutions needs to be developed by the learners. This notion of
appropriate challenge also aligns with the Zone of Proximal Development (ZPD) (Vygotsky, 1978). Similarly, the National
Council of Teachers of Mathematics (NCTM) (2014) noted: