Lego has managed to maintain its status at the toy for future doctors and ambassadors, even as what constitutes a “good” toy has evolved. In the late ’90s, toy-makers responded to parents’ increasing desire for enriching toys by producing more overtly educational ones: interactive toys meant to teach spelling, math, and shape recognition. For a few years, those toys were the fastest-growing ones in the industry, until they weren’t. Child-development experts began to argue that they made children too passive and might actually hamper learning. Plus, as one toy-maker put it to me, “kids can smell an educational toy a mile away.”

Instead, play researchers argued that toys should foster more open-ended creativity and exploration — toys that forced the child to do the work, like Lego. Promoting creativity appealed to parents too; here was a skill that robots will never take over. Lego’s own research has shown that the newest generation of parents — the millennials who are just now having kids — are increasingly sensitive to what their toys can do for their children and value creativity in particular.

Whether Lego actually does foster creativity is almost impossible to say. It’s proved awfully tough to figure out how play, not least toys, actually contribute to smarts. There is research showing that kids who play regularly with blocks and Legos have higher standardized-test scores and higher math achievement. But there’s ammunition for the other side, too: A competing study suggested that Legos, by being prescriptive, can impede creativity. The authors went so far as to contend that even standard blocks might give kids too much information — arches, after all, suggest their use. (They argue for building with uniform planks.) Marvin Minsky, the MIT scientist who helped pioneer artificial intelligence, has even said that “the decline of American inventiveness” can be traced to the rise of Lego, arguing that by becoming the most common construction toy, it’s pushed out construction toys like Tinker Toys and Erector sets that can get kids building simple machines.