About 10 per cent are male, but the figure may be as high as 25 per cent among school children.
Anorexia and bulimia are most common among young women, generally developing between the ages of 15 and 25, though sometimes seven or eight. Bulimia is rare before the age of 13.
So how can schools help children to overcome any problems?
Do not expect classes informing pupils about eating disorders to have preventative benefits. The best protection against developing eating disorders is the general development of assertiveness and self-esteem.
Staff are the most likely group to benefit from education about eating disorders.
Show respect for meal times and snack times. Provide proper dining hall facilities and encourage provision of balanced meals, water and healthy snacks, rather than rushed, fast-food lunches or allow skipping of meals.
Don't turn a blind eye. Express concerns about overly thin pupils matter-of-factly.
Keep a special eye on athletes, gymnasts, actors and dancers.
Body-conscious subjects have a higher risk of encouraging eating disorders.
Discourage size bullying: extremes of weight are misfortunes, not crimes.
Think twice about taking severely underweight pupils on outward-bound trips or sporting activities.
Do not bend over backwards to accommodate anorexia in school. It may be healthier for a pupil to take a break from exams and other stresses while they recover, rather than continue to sacrifice their health for the sake of achieving high grades. Anorexia can make someone very immature, so they may benefit from repeating a year.
Schools can't be expected to feed anorexic pupils any more than they would take responsibility for administering medication, but they can facilitate meals. Providing a quiet, secluded room for the pupil to take lunch can be helpful.
Do not give any one particular pupil the role of looking after an anorexic pupil, especially if she or he is a sibling. This is an enormous burden on anyone, especially a teenager.
Strongly encourage pupils with eating disorders and their families to attend treatment sessions and make it easy to take time away from lessons to attend appointments discreetly. Most clinicians will ask for formal permission to communicate with a school: this can help the school and the patient.