Chronic fatigue syndrome affects one in 50 children, leading to mental health problems and missing school.
A therapy that successfully treats two-thirds of children with chronic fatigue syndrome is being trialled for NHS use.
The trial, on 734 children, will use intensive online therapy sessions to adjust sleeping habits and activity levels. It also uses a form of behavioural therapy to help children with the disease adapt the way they live.
Prof Crawley is leading the FITNET-NHS trial, to see if online consultations work and are cost-effective for the health service. It is being funded by the research wing of the NHS in England, but when the results are out all the devolved health services would then decide whether they wanted to introduce it.
Trials of the scheme in the Netherlands showed 63% of the patients given therapy had no symptoms after six months, whereas just 8% recovered without it. The scheme offers behavioural therapy sessions to change the way children think of the disease and aims to reduce the time spent sleeping and sometimes cut activity levels.
The approach regularly receives criticism from some activists who argue it treats chronic fatigue syndrome as a disease of the mind.
Prof Crawley said: "A teenager might say, 'You are just trying to change my sleep', but do you know how much biology you actually change? Children who come to my clinic have low cortisol [stress hormone] levels in the morning, that is why they feel so terrible; by changing their sleep, we reverse that. The stuff we are doing is not a pill, but it might as well be."
Mary-Jane Willows, from the Association of Young People with ME, told the BBC: "It is a scandal, what other condition would you leave a child with - undiagnosed and untreated? And the trouble is the longer they are left, the more ill they become.
Prof Stephen Holgate, from the Medical Research Council, said: "CFS/ME is an important disabling condition. "It has been chronically underfunded for years; patients deserve high-quality research like this."