By Gary Eason
BBC news, at the ATL conference in Torquay
Teachers want extra funding to cope with the numbers of children arriving from abroad with little or no English.
Migrant children need extra support in the classroom
The Association of Teachers and Lecturers (ATL) heard the problem had been brought about by the recent influx of refugee and EU migrant families.
It wants the government to provide additional support to schools accepting large numbers of children for whom English is an additional language.
The government says it is investing more money and resources in this area.
Joy Barrett - who works in Oxfordshire's ethnic minority achievement service - said that in 2006 across England there were some 66,000 more children with English as a second language, many of them new arrivals.
But she told the conference, in Torquay, that there was a lack of joined-up thinking about the issue.
It had been "sadly lacking" in remarks to the conference on Wednesday by Schools Minister Jim Knight, she said.
"We need special training for these students. If every child matters then these students need our support to access the curriculum and achieve their potential."
Coventry teacher Stephen Holmes said that in his area - as in many others - the number of children had been falling in recent years, leading to redundancies and school closures.
But the downward trend had been reversed, with the arrival of more than 4,000 children of immigrant families in six years.
More than 3,000 of them had been placed in primary schools - but not evenly.
The vast majority of newly arrived families had been placed in deprived areas with empty houses - and with spare capacity in the schools.
In each of the last two years more than 1,000 children had arrived in the first term, and a further 200 to 300 throughout the year. But not all stayed.
"Mixed in with the unpredictable growth is transience on an enormous scale," Mr Holmes said.
"Day after day the elasticity of the teachers and support staff is tested as they plan and deliver lessons for groups with over a third of the children for whom English is a second language."
Yet they were challenged by "the same old targets" to produce results and, as ever, "just a hair's breadth away from being labelled as failing".
He said: "It's about time we stopped hiding the problem behind classroom doors, challenged the government's glib euphemisms and insisted that despite its complexity, the problem must not be ignored."
Another Coventry teacher, David Kinnen, said it was not fair on the children.
Last Friday he had been asked to teach a science lesson to 10 youngsters aged 15.
One had multiple special needs and the other nine had English as a second language.
One girl, who was from Afghanistan, spoke no fewer than six languages.
"And yet she is in set eight out of 10 for science: there's something seriously wrong there," he said.
The fact that some children struggled with basic English and other special needs made "a time bomb".
"What we had there was not setting by ability but setting by language, setting by behaviour and setting by special educational needs.
"This was a sink group."
A DCSF spokesman said: "We have listened to these concerns and are increasing funding in the Ethnic Minority Achievement Grant to £206m by 2010.
"Alongside that we've also introduced new guidance for teachers to work with new arrivals.
"We recently carried out a consultation, including ATL, on how to release funding when needed - for example during the term, if an influx of migrant children arrive and will make allocations later in the year where needed.
"Extra funding for schools is worked out on a targeted formula based on numbers of pupils with English as a second language, who are from deprived areas and who have been identified as needing additional support."
The DCSF said that by 2010-11 there will be more than £300 million in general school funding for children with English as an additional language.
And there had been a general increase in money spent on education - up by more than 60% in real terms since 1996-97, the spokesman said.