The schools - all with high educational needs - will be used in an experiment to test the impact of reducing class sizes on pupils and teachers. The proposal is outlined in a 20-page policy statement drawn up by Win Griffiths, shadow education minister for Wales.

The Welsh document speaks of a “new partnership for all schools, including those which are currently grant-maintained.

“We will ensure that all schools are equitably funded, operate an agreed authority-wide non-selective admissions policy and are locally accountable in partnership with their local education authority.”

There are only 16 GM schools out of nearly 2,000 in Wales - the policy statement says that within local management, heads and governors should be able to develop “the distinctive character and particular strengths of their schools”.

Labour pledges to extend nursery provision, co-ordinated with childcare, for all three and four-year-olds and proposes an inquiry into measuring school effectiveness. All schools would be required to publish annually exam achievements for the previous three years, while local authorities would have to detail their own performance.

Teachers would be encouraged to top up their skills and build up credits from professional development courses, while school inspectors would be expected to maintain regular classroom experience.