Children could be forced into "double-bunked" mega schools under Education Act changes.

One of the country's biggest schools is already considering its options after changes that allow boards to set new start times - meaning they could offer morning and afternoon programmes from the same school, effectively doubling student numbers.

The time-shifting changes are covered in the Education Amendment Bill, lodged in Parliament last week, and extend nationwide the flexible timetabling allowed in Christchurch schools after the Canterbury earthquake.

The bill also introduces charter schools, proposes the development of national student numbers, and gives teachers the right to seize and search student cellphones.

Mt Albert Grammar School headmaster Dale Burden says flexible timetables could be useful for popular schools operating at capacity. "Given the demand we have and the growth - we have around 2000 students but could easily have 4000 who want to be here - it would work.

"It is sensible in one way, because schools close at 3pm and there are all these unused rooms until 9am the next day," he said. "From the ministry's point of view, you could agree a case for a better use of resources."

He said Mt Albert had not made any decisions, and there were disadvantages that needed to be weighed up - such as curtailing sport and activities - but he said giving schools the ability to think outside the square was a benefit, and predicted a minority would change.

"It might suit some schools, and loosening the legislation makes that possible. If it's what the community wants, that what's important."

An Education Ministry spokesperson said no one expected any board to propose moving all its students to consecutive timetables. "But there could be demand from the community for timetable options well outside the traditional 9am-3pm norm. Multiple timetables might also allow schools to get more benefit out of specialist classroom space, such as technology classrooms."

Auckland University education associate professor Tim O'Connor said changes could be forced on unwilling communities. He said despite the ministry promoting flexible timetables as pro-community, it wouldn't be difficult to change legislation and require boards to follow a ministry directive.

"I'm sure Education Minister Hekia Parata will be saying she's consulting and working out the finer details, but what the Government tends to do with education policy is release it, scare everyone, and then work out the details.

"Part of the problem is releasing policy without any details so that people respond and then they scramble behind the scenes. The classic was classroom sizes, then the next debacle was league tables, and then Christchurch," he said referring to proposals to close or merge many Christchurch schools.

He said the Government would put up a financial argument for different timetables at one site, but what emerged at the end of the consultation would not necessarily be what was proposed. "This seems to be based on a political agenda around what the ministry sees as best. Part of that is disconnecting schools from communities. Schools aren't just places you get qualifications, they're the glue for communities. When you tear that apart, you get wider social issues."

The ministry said boards would have to consult with parents, staff, and the community about proposed multiple timetables.