Roald Dahl's books were awesome! I loved BFG, Mathilda and Danny, The Champion of the World when I was a kid because they were really imaginative. I also read the Fighting Fantasy and Grailquest gamebooks back then - I can't say that my English dramatically improved from reading the loonyness/looniness is Grailquest, but they sure made me love reading.

Does your son enjoy reading any particular category of books - adventure, fantasy, sci-fi, etc?

The BFG is one of his favourites.
He really liked Charlie & the Chocolate factory, but when it was on TV today he declared the film "BORING"!

He's very into fantasy adventure.
Some ofthe Beast Quest books have a "Choose your own Adventure" format.
I did get him a couple of Fighting Fantasy books, but they didn't go down so well.
He's a bit of a sore loser.
He's at the age where everything is a competition.
He hasn't yet discovered the fun of playing for the sake of playing.
He's the same with football, board games, everything!

Have you finished the series yet ? I need to read the last book.

Finished all of what's been released, but the final book doesn't come out until this coming May.

I fondly recall some adult swim(Cartoon network late night lineup) show or other(Family Guy maybe?) where one guy said he loved the Hardy Boys and another guys said "Oh but all their stories are the same, they're all about smuggling." to which the first guy replies "But not the story about the pirates at smuggler's cove.....that's about pirates."

:)

If Roald Dahl is within his reach, then these should also be suitable:

Lynne Reid Banks, The Indian in the Cupboard series.

E. B. White, Charlotte's Web.

If Roald Dahl is a little too much for him, try:

James Preller, the "Jigsaw Jones" mysteries.

Jon Scieszka, The Stinky Cheese Man; the "Time Warp Trio" series.

I don't know how I could have forgotten about this. In fact, my 10-yo little brother has a copy lying on my study table. I've flipped through it and it is definitely very readable even at my student's standard.

Beverly Cleary's boy books (like the ones with Henry or Ralph the talking mouse) and Judy Blume's Peter & Fudge books?

Almost every single kid tends to love Roald Dahl books, which is awesome for trying to get them to enjoy reading, but the downside is.... he's so..... British. Not sure if that might matter in Singapore.

I always had the hardest time getting students to grasp grammar. It's just not something that'll get fixed quickly.

Lewis Carroll's Alice in Wonderland is great for both younger and older English language learners. It's basic language is founded on easy vocabulary and simple grammatical constructions, yet advanced learners will appreciate the elaborate word play and linguistic riddles, especially in Through the Looking Glass. Also, it's a literature classic.

Have the Narnia books been mentioned? Or the Terry Pratchett books "for younger readers" (Tiffany Aching series and Amazing Maurice + educated rodents) ?
I remember loving the "Deptford Mice" books as a child, and also seem to remember reading a very good book which had a lot of more complicated linguistic concepts packaged in a nice way -- I think it was called "The Phantom Tollboth"?

I'm not sure what the reading levels of these are, but I hope it helps :)

My 12 year old thinks Patrick Carman's The Land of Elyon Books would be perfect.
What I previewed of the books. They seem to be an easy read.

http://www.amazon.com/Dark-Hills-Divide-Land-Elyon/dp/0439700930