The La Salle schools in Kowloon are among five pairs of top English-medium schools that have to decide by May next year whether to form through-train schools or sever the historic links between their secondary and feeder primary schools.

Under the through-train policy they would have to admit all students, regardless of ability, from the primary school. But this, they believe, would make it difficult for the secondary schools to fulfil conditions proposed by the Education Commission to be able to continue teaching in English.

Only schools that admitted at least 85 per cent of students able to learn in English would be allowed to remain English medium from 2008, under proposals by a commission working group on medium of instruction and school places allocation. These students are defined as those in the top 40 per cent of the ability range.

The principal of La Salle Primary School, Elizabeth Pau Chan Wai-yee, said this would be impossible now that the primary had to admit mixed ability pupils.

If they don't become through schools and break the links, the secondary schools would no longer automatically admit those who meet their requirements - about 90 per cent for La Salle Primary.

Tony Wong Shou-fat, chairman of La Salle Primary's parent teacher association, said: 'I would move my son overseas. Some have already done so. It is a big concern because the method of deciding if a school remains EMI will depend on the performance of the primary. No school can reach that target.'

Paul Lau Wai-keen, principal of La Salle College, said: 'There is no guarantee that we could achieve 85 per cent [of students capable of learning in English]. If we have to meet the target that poses a threat, to our parents and school if we want to maintain our traditions.'

Mrs Pau is concerned about the effect that either de-linking or forming a through school will have. If it forms a through school, the primary and its students would be under greater pressure to ensure all were among the top 40 per cent.

'Even if boys' results don't affect their places they will affect others in years to come. Teachers will have to push them harder, and maybe drop some extra-curricular activities,' she said.

Mrs Pau has proposed that the deadline for switching to a through school be delayed until 2012, to allow the language policy to be implemented first and to give the college time to assess the new primary admission policy.

An alternative would be to delay implementing the language policy to give the schools more time to prepare, or to reduce the threshold of 'English capable' students from 85 per cent to 65 to 70 per cent.

Mrs Pau was among representatives from the Grant Schools Council who met with Michael Tien Puk-sun, chairman of the working group, last week.

The council's chairman George Tam Siu-ping, principal of Wah Yan College, said there was a contradiction between the language and through-train policies. 'Many English-medium schools will be discouraged from forming through schools,' he said.

'We may have to switch away from emphasising happy learning and whole-person development, and drill students in Chinese, English and mathematics.'

Mr Tien said he was prepared to negotiate on the timing of the changes, but not the educational principals of the language policy. 'I promised we would recommend to the Education Commission that the deadline [for forming through schools] be delayed, because it is very unfair to them,' he said.

He dismissed concerns that the policy could increase pressure on primary children. 'If you have to learn in English you have to work harder and go through a more rigorous primary curriculum,' he said. Pressure in the top schools was nothing new. 'It has always been around. We didn't create it.'

Other English-medium secondaries that have to decide whether to form through schools or de-link from their primaries include St Stephen's Girls' College, Heep Yunn School, St Rose of Lima's College, and St Paul's Secondary School.