More than half of secondary schools support the authorities' proposal to reduce class size by up to four pupils per class over the next three years, education chief Eddie Ng Hak-kim says.
School principals have suggested cutting back on the number of pupils by six in that time.
The standard class size now is 34, although schools are allowed to enrol up to 36 in a class by using up two extra places meant for repeat pupils.
The clock is ticking for the enrolment mechanism to be finalised for next year, when the Form One population will start dropping because of low birth rates and by 2016 will have 11,000 fewer pupils than this year.
Educators have suggested a "3-2-1" reduction over three years, meaning decreasing class size gradually by three pupils in the first year, two in the second and one in the third year.
Education Bureau officials have counter proposed "2-1-1" or "1-1-1", depending on the needs of schools and districts.
Earlier this week, some of the principals backed down from their initial suggestion, agreeing with the bureau instead. Ng said yesterday the bureau's idea struck a balance between the concerns of various education stakeholders. "Other than those from the education sector and parents, many professional groups, including alumni [of secondary schools], have given us many opinions," he said.
The bureau will conduct a centralised allocation exercise for secondary school places at the start of next year. Before that, as a formality, the Secondary School Places Allocation Committee must approve the final enrolment mechanism, which it will do at a meeting on Wednesday.
The government says dramatic cuts in class sizes across the board would reduce opportunities for parents to secure places for their children in elite schools.
Many teachers prefer smaller classes and support a six-pupil reduction. The Professional Teachers' Union is threatening to launch a "disobedience movement", including having teachers refuse to submit data such as pupils' assessments to the Education Bureau.
Education-sector legislator Ip Kin-yuen, who is also the union's secretary general, said a reduction of one or two pupils in the coming academic year might result in some popular schools maintaining their current class sizes by giving repeat places to new pupils.
"The problem will only remain with the current proposal," Yip said.
Ng said the proposal would be reviewed. "Some people in certain districts are particularly worried. I suggest a review one year after the policy implementation."