Teachers have voted overwhelmingly in favour of strike action over a threat to pensions – a move which could lead to millions of children being sent home from school later this month.

The decision by members of the National Union of Teachers (NUT) and the traditionally moderate Association of Teachers and Lecturers (ATL) will force thousands of schools to close on 30 June – the date for the first strike action – with the prospect of more strikes to come in the autumn.

Both state and independent schools will be hit, with some leading private schools being subjected to industrial action for the first time.

Teachers will be joined by college and university lecturers – whose union, the University and College Union, has already voted for strikes. In all, 600,000 teachers and lecturers will be involved in the action.

Head teachers' leaders, who will decide later this week whether to carry out their own ballot for strike action, have already warned schools will close if there are not enough staff on hand to look after the children.

Russell Hobby, general secretary of the National Association of Head Teachers, said: "Health and safety of pupils will be paramount. If they can keep the school open they will: if not the school will close for the day."

Civil servants will also be staging strike action on the same day forcing unemployment and benefit departments to close and some Whitehall offices to come to a standstill.

Yesterday, members of the NUT registered a 92 per cent vote in favour of strike action with 86,246 voting in favour and only 6,918 against. The turn-out of the 218,370 members eligible to vote was just over 40 per cent.

ATL members voted 22,840 in favour and 4,653 against in a turn-out of 35 per cent. The vote in independent schools for strike action was just as strong as in state schools with 4,444 (83 per cent) private teachers in favour and only 868 against.

Mary Bousted, general secretary of ATL, said: "This is a warning shot across the bows of the Government. If even members of the least militant trade union and teachers in independent schools vote to strike the Government would be wrong to ignore it."

Under the proposed changes, teachers' pension contributions will go up from 6.4 per cent to 9.8 per cent. In addition, the retirement age will eventually be increased to 68 and there will be a 15 per cent reduction in the size of the pension. Teachers in independent schools may no longer be eligible for the scheme – which at present covers all schools in England and Wales.

A third teachers' union, the National Association of Schoolmasters Union of Women Teachers, could also join the dispute.

Streaming returns to the classroom

The controversial practice of "streaming" primary school pupils is making a return to state school classrooms, according to research published today, writes Richard Garner. One in six primary school pupils is now "streamed" by the age of seven, researchers at the University of London's Institute of Education have found.

Under the system, pupils are put in a stream for all subjects. The method of teaching was widespread in primary schools in the 1950s and 1960s as pupils competed for grammar school places.

Both setting – where pupils are put in a different set for different subjects – and streaming had been phased out in most schools by the early 1990s in favour of mixed-ability teaching. The Blair government was anxious to see a return of setting but was against streaming on the grounds that pupils had different levels of aptitude for different subjects.

Professor Sue Hallam, leader of the research project, criticised the return of the practice. "Once in a stream, the opportunities for movement to another stream are limited, so life chances are being determined at a very early age," she said.

The research showed that more than six in 10 of those streamed at seven were later moved into different ability sets for maths and English, and that girls were over-represented in the top stream, while boys were more likely to be in the middle or bottom streams.