Primary School (K-2)
Because there is always more than one possible solution to a problem, it is useful to compare and test designs.
Elementary School (3-5)
Different solutions need to be tested in order to determine which of them best solves the problem, given the criteria and the constraints.
Middle School (6-8)
Although one design may not perform the best across all tests, identifying the characteristics of the design that performed the best in each test can provide useful information for the redesign process - that is, some of the characteristics may be incorporated into the new design.
The iterative process of testing the most promising solutions and modifying what is proposed on the basis of the test results leads to greater refinement and ultimately to an optimal solution.
High School (9-12)
Criteria may need to be broken down into simpler ones that can be approached systematically, and decisions about the priority of certain criteria over others (trade-offs) may be needed.