Students have always faced distractions and time-wasters. But computers and cellphones, and the constant stream of stimuli they offer, pose a profound new challenge to focusing and learning.

Researchers say the lure of these technologies, while it affects adults too, is particularly powerful for young people. The risk, they say, is that developing brains can become more easily habituated than adult brains to constantly switching tasks — and less able to sustain attention.

“The worry is we’re raising a generation of kids in front of screens whose brains are going to be wired differently,” said Michael Rich, an associate professor at Harvard Medical School and executive director of the Center on Media and Child Health in Boston.

For some, the technology amplification is intense. Allison Miller, 14, sends and receives 27,000 texts in a month, her fingers clicking at a blistering pace as she carries on as many as seven text conversations at a time.