Professor Cheng, who was yesterday named as the institute's acting vice-president for research and development, was speaking at a school representatives' seminar to discuss the future of the city's primary education, attended by 190 principals and teachers.

He attributed the 'bottleneck' to school assessments and measures to introduce accountability to schools under the education reform in the last eight years. He said implementing them within a short time had left many teachers 'burnt-out'.

'At one stage, we had school-based management, increased parent participation in school policy, the drive for continuing learning, school-based assessment and outsourcing services, and so forth,' he said.

'These, combined with the pressure from the 'school-killing' policy, led teachers to do many tasks unrelated to teaching. So our schools failed to function normally.'

Professor Cheng said smaller classes could help relieve this 'bottleneck' by easing the tensions teachers faced and allowing them to concentrate more on teaching.

He also urged policymakers to devise ways to boost students' motivation, an area in which he said local students scored poorly in many international assessment studies. He said teachers had to adjust teaching methods to better address individual students' needs in small classes.

'Encouraging individual participation, helping students develop their own character and fostering civil education, are goals in our curriculum which schools can now work to achieve with this opportunity.'

Professor Cheng cited the 2006 Programme for International Student Assessment study, which ranked Hong Kong students second in scientific literacy, third in reading and equal third in maths literacy. However, the study of 57 countries and regions - released in December - put them close to the bottom in terms of self-esteem and motivation.

The HKIEd academic said another area primary school educators had to tackle was the medium of instruction and language education.

He said pupils' command of languages could be much improved if the medium of instruction was designated at the lower primary level.

'If schools can start learning Putonghua in lower primary... and build up confidence in communicating in English early, it will definitely make a difference to their future,' he said.

To improve the city's primary education, Professor Cheng suggested the government review the pace of reforms, relax the policy of closing schools and draw up long-term strategy to restore teachers' image and confidence.