An association organized on an individual school basis, made up of staff and parents, for the purpose of discussing and acting on a number of school‐related issues. These may include anything from organizing events to raise funds for the school, to the debating of educational issues such as those raised in an inspection by Ofsted. It is often run by a committee to which nominated parents are elected by ballot. The extent of its activities and the robustness of its membership will vary from school to school, and will often be dependent to some extent on how far such an association is encouraged by the head teacher and governors. Such an association does not exist at all schools. There is, however, a National Confederation of Parent–Teacher Associations, which acts as a platform for the views of its constituent members.
http://www.ncpta.org.uk/informationlist/100006/100180/starting_a_pta/ Details from the National Confederation of Parent–Teacher Associations on how and why a PTA may be established.