Evidence for slowing as a function of index of difficulty in young adults with Down syndrome.

Lam et al. (2009) asked young adults with Down syndrome to tap or point at targets that got smaller and farther away. The task is called Fitts' law — the harder the target, the longer it should take everyone.

They compared the speed and accuracy of adults with Down syndrome to same-age peers without disabilities.

Adults with Down syndrome moved about twice as slowly, but their speed-accuracy trade-off looked the same as controls. Harder targets slowed both groups in the same pattern.

The motor system works the same way; it just runs in slow motion.

Capio et al. (2013) and Falcomata et al. (2012) extend this idea to walking and memory. When people with Down syndrome walk while talking or remember while counting, they slow even more. The same slow-but-steady rule applies across tasks.

Eussen et al. (2016) seems to disagree. They found that preschoolers with Down syndrome give up waiting faster than peers, hinting at poor self-control. But the kids were much younger. By young adulthood the motor system has matured; it stays slow yet predictable, so the "impulsivity" gap closes.

Salami et al. (2014) show the same preservation in walking energy: adults with Down syndrome take shorter, slower steps but waste no extra fuel. Together the papers say "slower" does not mean "sloppy."

Give clients with Down syndrome at least double the usual response window when you teach buttoning, typing, or tablet swipes. Keep difficulty the same; just stretch the time. The skill will look like everyone else's, only later.