The government's education plans have been criticised after it emerged that hundreds of schools being offered a fast-track to academy status are the most socially exclusive.

An analysis by the Observer found that secondary schools judged as "outstanding" by Ofsted are taking 40% fewer poor pupils than the national average. Michael Gove, the secretary of state for education, has written to all schools inviting them to apply to become academies, a move that will free them from local authority control.

However, he is particularly urging "outstanding" schools to join the scheme and has approved them all in advance. "We specifically want to provide opportunities for outstanding schools to open as academies as early as September 2010," he wrote to headteachers.

Campaigners are warning that the policy risks creating a two-tier system in which resources and attention are focused on the most middle-class schools.