The survey, conducted from mid-October to late last month, found that more than two-thirds of the families were living in cubicles of between 51 sq ft and 150 sq ft in size.

One-fifth of the parents said their children "often" could not sleep well because of the crowded living environment. More than half of the parents believed quality of sleep would "strongly" affect their children's learning or their desire to learn.

Eighty-one per cent of parents also said the living space was too small for a desk at which their children could do homework.

Kaki Lam Man-wa, a spokesman for the alliance, said: "Many of the children cannot invite classmates back home to play or do homework together because of the poor living environment. It can strip them of the chance to make friends and that affects the children's personality growth.

"Very often, children from poor families lag behind their classmates academically because they do not have a proper place to do homework and cannot afford to take part in extra-curricular activities."

She called for a monthly extracurricular activity subsidy of HK$200 for needy children.

"The government should also eliminate subdivided flats as soon as possible and rehouse the residents to public housing," Lam said.

There is no legal definition of a subdivided flat, but the term is commonly used to describe cases where one flat is partitioned into two or more self-contained cubicles. Many of the conversions are carried out illegally.

They are often the only option for poor families, especially those not eligible for public housing.