There is a Pupil Premium as well as Pupil Premium Plus. The qualification for PP funding is whether a child is or has been eligible for free school meals within the last 6 years. PPP funding is for children who either are in care currently, or left care via a residence order, SGO or adoption order.
It's very important that you let the school know that your child is adopted and can get PPP. Adopted pupils eligible for PPP are identified via the school census, in January, for funding in the next financial year. So for funding from April 2015 to March 2016, the child must be indicated as adopted on the school census in January 2015. The onus is on you to let the school know in advance of them completing the census. If you miss the deadline, that's it till next year. If your child moves schools, you must let the new school know, again by the deadline.
The aim is that the money should be used to support eligible pupils, helping them achieve their full potential. Obviously all children are different, and so there are many ways the money could be used. A good school will be engaged with the parents in the process of finding ways to support the child, and how the PPP might be used. You can ask to meet with school if you want to discuss this. It is the schools responsibility to spend the money for what it has been intended to do.
The money is not ringfenced and it doesn't have to be all used on an individual child, however the school are accountable to OFSTED. In some cases, the money might be totally spend on things that are very individual for a particular child. Other times it might be considered a good idea to, for example, use money to send a few teachers on a training course in how trauma presents in the classroom/attachment/etc, if that would help the child indirectly. Alternatively, sometimes a whole-class use of some money might be appropriate, as long as that intervention will definitely be benefitting the child the money is meant to support where they have a need (and OFSTED will want the school to show them that was the case). What the school must not do, is allow the money to be used for general stuff or just be swallowed up into the main 'pot', which will not help support the child. The spending must be targeted.
It is not limited to improving a childs academic attainment - some children might be doing well academically but have marked needs in other areas eg. emotional and social and the school can use the money in that area. Nor does it have to be done within school - the school can pay a third party to provide something to the child which will benefit them.
The Sutton Trust's pupil premium toolkit can be used by the school. It shows schools which kinds of interventions are supported by evidence etc
Your childs school should involve you in deciding on how best to use the money to support your childs individual needs, though not all schools are actually on-the-ball about this, or good at communicating. Absolutely schedule a meeting with them about it if you need to discuss it.
A poster called tethersend knows a huge amount about education and how this all works, so hopefully she will be able to help