Depending on what is the 6th grader up to? This is one really funny, easy-to-read, and refreshing book. My 7-years-old daughter just finished reading both volumes of the wimpy kid, and she just loved them!....So much, that she even got every one in the family to laugh at a couples of the stories.
I also explored the book before handing it to her,-just to make sure it was appropriate-, and I has to confess, loved it myself,....My favorite character?? Manny! (The baby brother)....Just as a naturally very maternal and protective mother!...Loved the little one, so cute and special!...Rodrick? Just remind me of my husband coolness!....
In Sum, if the 6th grader is more toward mystery, like "twilight" tipe of lecture, probably would get not enjoyment out of this Kenney's books, I personally try to refresh life with good sense of humor, and like my daugter to grow up with a different sense of real life as well.
I think she would, provided she likes to read books in general. If she's not a big fan of reading you'd be better off getting her books related to her interests, such as specific hobby books, or history, fashion, science, whatever she's into. My little girl is 9 years old and she loves to read anything she can get her hands on....these books are her latest favorite. She was counting down the days until Dog Days was released last month. They're funny and not really 'little kid' material, so I think she'd enjoy it.
My 7 year old daughter loves this book, and so do I! I read it to her at bed time and also have her read it to me (we alternate paragraphs). I personally can not wait for our bed time reading - this is not like reading another kids' book, it is totally great reading for the adult as well! Love it.