How to decorate over this surface

[rborob]

Hi all,
I'm decorating my sons room and took the lining paper off a particularly bad wall. However, underneath were some boards which were just flaking. It's difficult to explain, like plasterboard which is peeling.
I've attached pictures to help.
I'm after advice on how best to prepare it for painting..should I plaster over it? Or sand it down and paint it??
Help is appreciated!

 

[Robbie uk]

That surface has been dry lined. This means that its made of plaster board which hasn't been skimmed with plaster. It makes it easier and quicker to fill the joints and paint. However when its papered and then stripped off it brings off the paper surface of the plaster board. In a word " A nightmare " Really needs skimming to make a proper job and start again.