Friend's dc have been there and seem to like it. However I'd suggest it probably isn't the most academic of options and if you have aspirations towards 11+ it may not be the best choice as they will want them to go onto their senior school.
I'd agree with LIZS - I know several children who go there.
No guarantees for Wallington Grammar, I'm afraid. Anyone can apply at the moment, so they get around 40 applications per place and give them to the top performers, regardless of where they live or have been to school.
There are some excellent state primary schools in Croydon LEA though - where do you live?
I am in east croydon...I heard about Park HIll - and went to see Croydon High recently - dont want to pay from 4 yrs for private (as very expensive esp if have naotherc hild will have to take her out).....
Wallington Grammar is a boys school. Do you mean Wallington Girls? It is very difficult to get into there. As someone else said, they take the cream of the applicants from wherever. Doesn't mean you can't try, though