BOX 4.4 Solving a Problem Children 18 to 36 months of age are given nesting cups to play with (DeLoache et al., 1985b; see also Karmiloff-Smith and Inhelder, 1974, on children balancing blocks). Five plastic cups are dumped on a table in front of a child, who is simply told, "These are for you to play with." Although the children have previously seen the cups nested together, there was no real need for them to attempt to nest the cups themselves; they could easily have stacked them, made an imaginary train, pretended to drink from them, etc. However, the children immediately started trying to fit the cups together, often working long and hard in the process.      Overall, in their spontaneous manipulations of a set of nesting cups, very young children progress from trying to correct their errors by exerting physical force without changing any of the relations among the elements, to making limited changes in a part of the problem set, to considering and operating on the problem as a whole. This "developmental" trend is observed not only across age, but also in the same children of the same age (30 months) given extensive time to play with the cups.      Most important, the children persist, not because they have to, or are guided to, or even because they are responding to failure; they persist because success and understanding are motivating in their own right.