Parents in an east London borough who take their children abroad for more than six weeks in term time risk losing them their school place.
The Government is also considering tackling extended leave, possibly through fines for parents.
Lengthy overseas trips are mainly an issue for ethnic-minority families visiting relatives. Research by the borough has revealed that children pay a high price in terms of their schooling for extended leave - regarded as more than two weeks away during term.
Last year, 6 per cent of Tower Hamlets' Bangladeshi primary and secondary pupils were away at any one time. More than half stayed away for between five and 10 weeks and at least 14 pupils were absent for more than 25 weeks. The problem is at its worst in September - one of the best months in which to visit Bangladesh.
It is estimated that the Bangladeshi children fall behind by around twice as many weeks as they are absent. The borough's research showed that pupils taking extended leave were twice as likely to leave school without any GCSE passes. Almost half failed to reach expected levels compared to a third of those staying on.
The pupils performed at lower levels in all subjects, especially maths and English. They were also twice as likely to be assessed as beginners in English or as having special educational needs. Secondary pupils taking leave were generally placed in lower ability bands.
The borough is sending a leaflet to parents warning them of the possible consequences of extended leave. John Sinnott at Tower Hamlets research division said: "We can't stress to parents in hard enough terms not to do this if they value their child's education. We hope the threat of losing a school place will work. It's also a question of helping heads use every possible method to dissuade."
Avril Newman is head of Sir William Burrough primary. When she took over two years ago she found many children were away for six weeks or more. She said: "It soon became clear these children were our under-achievers. You can't eradicate this, it happens whether I give permission or not. But what I can do is speak very harshly indeed to those who consider it. By working with parents and helping them see the damage that can be caused we've seen a dramatic fall in numbers going away. This year we only had three out of 300 who did so."
When Ms Newman can't stop a child leaving, she insists they take work with them. She said: "If we know it's going to happen the child's teacher will assess their levels and put together a basic pack to try and bridge the gap a little bit when they return. Yes, it makes more work for teachers, but it's a lot less difficult than starting all over again with a child who has forgotton everything they learned a term ago. We need to educate parents into putting a commitment to their child's education first.
"That said, I never deny there's not an enormous enrichment about travelling to another country and visiting relatives in another culture. All I ask is that they do it in the holidays."