I foster.
Foster children should be treated equally to birth children, but that doesn't necessarily mean treated alike.
You have to have realistic expectations and an understanding of the child's background, which may have been incredibly chaotic.
For some children the primary education target is simply to attend school, to not get into fights. That's as worthy of success as another child's A grade.
Every foster child will have their own Personal Education Plan. This is set up in conjunction with school (every school should have a member of staff with special responsibility for looked after children), social services, the foster parents and the child. Many children need utter baby steps in order to just get back into the school building.
A child who is looked after will have experienced trauma. At the very least, they are no longer living with their birth parents. Whilst their experience with birth parents may have been beyond awful, the trauma of separation is as great for that child as for your own birth children, if they were suddenly removed from your care. Under those circumstances, learning can't happen until survival has started to happen.
For other children, a rigidly controlled environment (eg must have bedroom tidy etc.) gives them a secure boundary, a safe structure so they can try to find order within the chaos. Again, any behaviour support plan like that should be drawn up in conjunction with the child's social worker.
If you have genuine concerns that a fostered child is being treated like a second class citizen in the foster family, and these are friends of yours, please speak to them.
But be aware of the fact there are all sorts of reasons why things might look different.
A child may look incredibly scruffy because they are hanging onto the clothes which came with them, and refuse all the new clothes in their cupboards because they need that link to their past. Another child may have very rigid rules about changing clothing because they haven't been taught basic hygiene and they now need to learn it as a new concept age 16. Another may use filth as a defence against the further abuse they still fear because that was their life for so long.
Don't be too quick to judge the foster carers, and do bear in mind we won't be able to tell you the child's back story.