“The sea,” said Samantha. Those words are something of an achievement. Last year Samantha (not her real name) was assigned to an experimental class at Montague Street school for children who test as non-verbal in English and their native Spanish.

The Los Angeles school district once thought it had only a few hundred such non-speakers. But a computer check after an inquiry from a newspaper showed nearly 7,000 cases last year alone. Barbara Stanley, a speech specialist who led the class at Montague Street, says it is not uncommon to find children of five and six, of normal intelligence, who cannot name a picture of a cow or recognise colours. “I’ve had several who could not say their own names, ” she said.

Teachers suspect the problem is not confined to immigrant children, mostly Hispanic, who account for 95 per cent of their pupils. They now are trying to discover how many native English speakers also suffer from aphasia - a term usually applied to older people who lose speech after a stroke.

Delayed verbal development does not always spell a problem, of course. Einstein did not speak till he was four, Ms Stanley said, suggesting his genius and creativity were driving in other directions. James Earl Jones, the American actor known for his authoritative voice, was an elective mute as a child, and so was poet Maya Angelou.

But what drove Montague Street’s efforts was a child-tracking study showing the non-speakers were heavily represented among children who later fell far behind in reading and mathematics, and suffered discipline problems. In simple terms, if they could not speak, they could not learn.

An alarming drop in reading standards has driven a return in California schools to old-fashioned phonics teaching. But if a child does not have a particular word in its oral vocabulary, it is estimated that it takes four times longer to learn to read that word.

Early intervention, the school concluded, was the key to bringing the non-speakers into the educational system early before they were lost to truancy and gangs, and cut out of classwork by their inability to communicate. “We are the only chance these kids have got,” said Ms Pritchard.

The Montague Street school is in the San Fernando Valley, north-west of central Los Angeles, once orange groves but now suburban tracts of cheaper housing. The site where Rodney King was beaten by Los Angeles policemen is nearby.

The neighbourhood is dominated by recent immigrants from Mexico and South America, often illegal, with several families sharing a house and sometimes living in garages. Drugs and gangs are rife.

Many of the school’s 1,200 pupils are being cared for by grandparents or relatives rather than their parents. Some have lost fathers to shootings. But Ms Pritchard, in her four years at the school, has launched a series of grant-aided special programmes, including developing seven semi-autonomous “academies” in subjects from writing to computing, to try to raise standards.

Last year, 19 non-verbal children were placed in a class where specially-trained teachers focused on aural bombardment - talking them through a list of activities, from acting and singing to cooking, touching, and feeling, changing pace every 10 minutes to avoid losing their interest. It is believed to be the first of its kind in California.

Two of the children were eventually diagnosed as having mental or physical impairment, and later placed in special education classes. One boy had lost some hearing because ear infections had not been treated. Another silent child was removed from the school after teachers suspected abuse.

But most, like Samantha, have now joined regular classes. They have apparently suffered mostly from a lack of exposure to language in large families where books are scarce, parents are exhausted by hard and ill-paid work, and sanity demands that children keep quiet. The simple act of eating dinner as a family correlates more closely with children’s educational achievement than almost any other factor, the teachers’ research shows. Passively watching television is apparently no substitute.

The teachers at Montague Street are careful never to blame parents. Many attend classes, and are encouraged to join their children in class. Teachers encourage quiet parents to speak out, urging them to put signs in their homes, reading “Talk to your child”.