The Definition of Parental Responsibility 

In the UK there are two Acts which define this:

The Children's Act 1989 sets out what parental responsibility means and who has it. This will be the child's natural parents or those who have acquired parental responsibility through the courts such as a Special Guardianship Order or Care Order.

S576 of The Education Act 1996 defines parental responsibility as s3 Children's Act 1989 but extends the parental responsibility to 'anyone who is not the child's natural parents but is aged over 18 and has 'day to day' responsibility for the child. 

This can therefore include, step parents, foster carers, or extended family relatives. This means that for the purpose of education you have certain responsibilities and decision making abilities to ensure the child you are responsible for is suitably educated. It also means that if you fail to secure a suitable education you can also be fined and prosecuted if you fail to do this.