FEWER than half of 11-year-olds regard themselves as being in good health, according to a new survey carried out in Scottish primary schools.

Self-reported illnesses and symptoms at age 11, by both children and parents on their behalf, ran counter to any assumption of youthful healthiness, said researchers.

As well as physical illness, symptoms of emotional disturbance, such as irritability, anxiety, and unhappiness, were reported by over one-third of children.

The survey was carried out by Dr Patrick West and Dr Helen Sweeting from the MRC Sociology Unit at Glasgow University, and the results appear today in the Archive of Disease in Childhood.

The study looked at 2586 11-year olds from 135 primary schools in Glasgow and the surrounding area.

Only 47% described their health as having been good in the previous year. One in five reported a long-standing illness and 8% a limiting illness. Allergies were the most common complaint, with malaise (emotional symptoms) also common.

The authors suggest that illness among children may be underestimated because the wide age-bands used in routine statistics - up to four years old, ages five to nine and 10-15 - may obscure the real picture of age-based changes in health.

This meant that children and their parents - as well as professionals - might have a poor understanding of the needs of ''normal'' children, making health policy and planning difficult or arbitrary.

Children were questioned by nurses in classroom sessions and given a similar questionnaire to take home to their parents.

Parents were less likely to report conditions and symptoms than the children themselves. Concurrence was highest for conditions that were common, visible or diagnosed. The greatest disagreement occurred when it came to a child's emotional state, partly because it might fluctuate and may not be obvious.

The researchers said: ''In addition, high levels of disagreement may occur because a child chooses to hide feelings from parents, or because parents are unable or unwilling to recognise emotional distress in their child.''

The more salient an illness, the more accurately it would be reported, they point out.

Illness reporting was also subject to ''censorship'', with parents and children being governed by prevailing ideas about medical relevance or social desirability.

''Both parents and - even more so - children are aware of the 'nutty' stigma of admitting to psychological distress,'' said the researchers.

Given the subjects were at school, the high prevalence of minor infections was to be expected. More surprisingly perhaps, each of the malaise symptoms was described by a third or more of the children. Nervousness and irritability, for example, were each reported by about 40%.

''It is somewhat paradoxical that while the overall health of children has improved dramatically over the past century, only half of this group of 11-year-olds rated their own health as good,'' the study concluded.

However, the results were consistent with a recent study which found that high levels of poor physical and mental health in an older group of adolescents, followed up between the ages of 15 and 21, also matched the proportions in the 1995 General Household Survey in 5 to 15-year-olds, for whom the rate of long-standing illness had doubled over the past 20 years.

''This trend may have resulted from changed expectations of health and definitions of illness resulting from increased access to medical care,'' said the authors.

''However, it may also reflect a real increase in the prevalence of certain chronic conditions - the prevalence of asthma is rising, whether owing to an increase in parental awareness of symptoms and subsequent initiation of health service contact, an increasing severity of the disorder, or the impact of environmental factors.''

The high incidence of malaise also reflected evidence of substantial increases in psychosocial disorders among young people over the past 50 years, a pattern which has not been a continuation of previous trends.