Meanwhile, play, one of the most important ways through which children socialize and learn, can be daunting. What might come naturally to neurotypical children -- collaborating, taking turns, assigning roles and group decision-making -- can be a challenge for an autistic child.

One specific type of therapy for autism uses the humble plastic brick as its main tool: Lego.

As described by its originator, pediatric neuropsychologist Daniel LeGoff, Lego-based therapy has children work in small groups to build a Lego set. One student, the "engineer," has the instructions and directs the project. Another student, the "supplier," has the collection of Lego parts and hands them off to the "builder," who does the actual assembly. These roles rotate among the children.

LeGoff first conceived of Lego-based therapy when two of his patients -- eight-year-olds with Asperger's syndrome -- met in the waiting room of the clinic where they received treatment. Auspiciously, they had both brought Lego creations with them, and although both children struggled with social interaction, they were excitedly playing and talking with each other. LeGoff decided to incorporate Lego into therapy sessions for the two children; eventually, the group grew to seven. They moved away from set building and into free building and self-directed projects.

"LEGO-Based Therapy taps into core strengths in people with autism: their love of patterns, regularity, decomposing wholes into parts, predictability, understanding how things work, and creating variety out of structured manipulation of variables," LeGoff writes in his book LEGO®-Based Therapy: How to build social competence through LEGO®-based Clubs for children with autism and related conditions. "LEGO-Based Therapy uses such strengths in a social context, to make social learning fun and to play to the child's strengths, not their disabilities."

At its most sophisticated, a Lego team collaborates to create a narrative. It might, for example, make a robot and a shark and then direct a stop-motion movie of the two creatures fighting. This requires planning and division of labor -- and thus extensive verbal and nonverbal communication.

"When the Lego therapy is gelling, you almost have to sit there and just watch it, because the kids do their own therapy," said LeGoff. "It's why I often say that I don't take too much credit. They show up early, they're in the waiting room and they bust through the door. They have projects they want to get to and things they want to continue from last week."

"Kids who wouldn't normally be interested in taking turns, dividing the labor and negotiating are willing to follow the rules because they're able to get access to the especially cool Lego [set]," said GW Krauss, who interned and completed his postdoctoral work under LeGoff. He is currently an operational psychologist for the United States Army. "The child is strongly motivated [and says to themselves], 'I'm willing to do what it takes to be involved in this, because it's just so overwhelmingly fun.'"

"In a 150-piece set, there are 150 opportunities to talk about each piece."

"[Set building] typically only lasts for one or two sets," Krauss said. "Almost always, due to the nature of the project, children want to veer off, be creative and come up with their own ideas."

All of this -- the self-guided projects, the self-enforcement of rules and standards of behavior -- aligns with a general teaching principle that has gained steam in the past two decades: the importance of moving toward student-led initiatives and away from adult-led initiatives. In an ideal scenario, a teacher will facilitate the student's self-exploration rather than existing as the sole purveyor of knowledge.

The Lego-based therapy model is also forgiving toward the therapist, who has multiple chances to observe and model good behavior. "In a 150-piece set, there are 150 opportunities to talk about each piece. 'Is it the right one? Did we put it in the right place? What comes next?'" LeGoff said. "There's a lot of communication involved, a lot of replication and duplication. And for a therapist who's in the room to coach those interactions, there's a lot of opportunities to get it right.

"[The children will] actually start coaching each other on social stuff," LeGoff said. "One of the kids actually said to me, 'Dr. Dan, I need to get better at my social skills, because I'm never going to get my project done. I need to communicate more effectively.'"