Children with ADHD tend to avoid activities that require sustained concentration or that might be boring.

Any form of sustained concentration fatigued Reggie.

Wanting it more didn't refer to "desire," but to sustained concentration.

He knew from his own experience that Robin was capable of fearsome and sustained concentration on things that interested him.

Worthy said the difference was sustained concentration.

But he proved incredibly hardworking, gently amused perhaps by their common enthusiasm but capable of the sustained concentration which is the mark of a scholar.

It requires silence, some form of isolation, and sustained concentration in the presence of an enigmatic thing.

Read silently and with sustained concentration.

- but as proof of the writer's sustained concentration.

Staying "focused" means sustained concentration.