Like all specialist schools, they are allowed to select up to 10 per cent of their pupils according to their aptitude - in other words, by making choices based on pupils' potential rather than their current levels of ability.
It is unclear how many city academies have taken advantage of this power, although it is estimated that only 6 per cent of specialist schools make use of it.
The Department for Education and Skills has insisted that the opening of city academies should not have an adverse impact on other schools in their local communities.
In practice, most pupils who used to attend the schools which the academies replaced have tended to transfer to them. However, academies are not under any legal obligation to give preferental treatment to pupils who live closer than others.
The Sandwell academy, which will open in 2006 next to West Bromwich football club, will have catchment areas at the centre of each of the borough's six towns: Oldbury, Rowley Regis, Smethwick, Tipton, Wednesbury, and West Bromwich.
City academies are obliged to consult on their admissions policies locally and then have them formally agreed by the Secretary of State for Education.