On a recent Sunday, while Walt was baking gluten-free cookies, his mother had to remind him to check the recipe, put the eggs away, and close the refrigerator door. But he navigated the oven and timer just fine, and carefully used a spatula to shift the warm cookies from the baking sheet to the cooling rack.

A few minutes later, after a quick, reassuring hug, the 16-year-old resumed the scrapbook he had started that morning, printing out pictures of his favorite Theodore Tugboats, trimming them to fit, and labeling each one.

“I did so awesome,’’ he said excitedly when he was done. He piled five of the now-cool cookies onto a plate, hurried off into another room, and crooned Christmas carols to calm himself down.

Life with Walt alternates between moments of enthusiasm and anxiety, scowls and spontaneous hugs, typical teenage behavior and younger-than-his-age interests.

Diagnosed with autism as a preschooler, Walt went through years of temper tantrums, diarrhea, skin scratching, unpredictable behaviors, and obvious physical pain. A few minutes spent at his airy Groton home reveal both that Walt, now 5 feet 6 inches tall, is not a typical teenager, and that he and his family - including two siblings not on the autism spectrum - manage his challenges with good nature, warmth, and lots of humor. Like many parents of autistic children, Walt’s mother, Sarah Connell has often been ahead of his doctors and caregivers in coming up with new ways to help him.