Mr Wu said through-train schooling could relieve examination pressure on students at the lower levels and was conducive to nurturing students' creativity.

He said there was resource sharing and exchange among kindergarten, primary and secondary schools. For example, some primary school teachers gave kindergarten lessons, while some kindergarten teachers had been asked to deliver primary school lessons.

The practice ensured continuity of teaching in different phases, he said, but admitted the school faced some difficulties with the through-train concept.

'Since we do not select pupils, there is wider mix of students' abilities within a class,' he said. But this should not discourage teachers. 'We can try to narrow the gap,' he said.

The learning gap between pupils of differing abilities has been a source of complaint from some teachers at Shanghai's through-train schools. But Mr Wu believed the schools enjoyed more benefits by taking care of students with mixed abilities.

'We can look carefully at the development of pupils from kindergarten and take necessary measures to narrow the gap among students,' he said.

Through-train schooling was a notable feature of schooling, he said.

Hong Kong's Education Commission has noted the example of Shanghai, where there are now 74 through-train schools. In its consultation paper released in May last year, the commission recommended the widespread introduction of through-train schooling.

But University of Hong Kong education department associate professor Dr Ng Ho-ming said teachers at through-train schools found their job harder than those in streamed schools, because they had to deal with students with a wide range of abilities.

'Through-train schools in Shanghai are not doing that well in this regard and there has been some frustration among teachers,' he said.

There was no conclusive evidence to show the quality of through-train schools was better than ordinary schools.

Commenting on the teachers' complaints, Shanghai Municipal Education Commission deputy director Zhang Minsheng said: 'Why can't the teachers change their attitudes over students' welfare? We should have the welfare of the majority of students in mind when we assess education policies.'

In Hong Kong, some elite schools have expressed reservations about through-train schooling, citing difficulties in catering for a wider mix of abilities. Dr Ng said some of these schools might not be interested in adopting the system.

'In the past, these schools could select the top students, but they would no longer be able to do so if they were linked with a primary school,' said Dr Ng, who organised a teachers' study tour to Shanghai in December.

Jian Qing School has been seen as a model of through-train education. When set up in 1984, it incorporated the nine years of primary and junior secondary schooling.

In 1996, the school set up a kindergarten within its campus, lengthening the schooling on offer to 12 years.

In 1997, the school extended its 'through-train' to 15 years by setting up an extended class to enable about 50 junior secondary students to go straight to senior school without having to sit public examinations.

The school has 2,500 students, of whom 1,700 are secondary students and 800 are at the primary level.

Since 1996, all junior school places in Shanghai have been allocated through neighbourhood attendance.