Jacob Trigg was barely three years old when his mother, Pamela, began to notice he was not quite like other boys. While his classmates ran amok in preschool, he would find a quiet corner and sit by himself. At the age of four, he begged to leave restaurants, refused to play sports, and showed little interest in making friends. It took several adults to hold him down for a haircut.

For most toddlers, tantrums and clumsiness are just a part of life, something they grow out of. Yet a burgeoning number of parents, like Pamela Trigg, are reporting that their children exhibit baffling, intense behaviors. Some overreact, recoiling from loud noises or refusing to wear itchy clothes. Others underreact, showing little reaction to pain or crashing their bodies into walls.

In the last decade, tens of thousands of children have been labeled with sensory processing disorder, a once-unheard of condition which advocates liken to a neurological “traffic jam” that prevents the brain from handling external stimuli and making sense of certain sounds, sights, smells, tastes, and textures. The Sensory Processing Disorder Foundation, a 35-year-old research and advocacy group based in Denver, claims SPD disrupts the everyday lives of more than four million Americans.

Many families find such behavior so debilitating that they are hiring occupational therapists to teach them how to play with their kids or to brush their skin with soft-bristled brushes. Across the country, clinicians charge as much as $200 an hour to encourage children with sensory problems to spin in slings and hammocks, play with shaving foam, and blow bubbles through a hose.

For some, this is sheer quackery. There is still little consensus within the medical community on whether SPD is an actual disorder, let alone whether many popular treatments work. Last year, the SPD Foundation failed in its decade-long campaign to convince the American Psychiatric Association to include SPD in the fifth edition of Diagnostic and Statistical Manual of Mental Disorders. In 2012, the American Academy of Pediatrics claimed it is unclear whether children with sensory problems have a distinct disorder or whether their challenges are linked with other disorders such as autism, ADHD and anxiety. It urged doctors to caution parents that the effectiveness of sensory integration treatments are “limited and inconclusive.”