This is one of the favorite all time series in my classroom. The dark humour and excellent use of language and vocabulary is excellent for students (and adults) of all ages. Highly recommend for grades 3 and up.
Love Pratchett, and love this young adult series. Tiffany Aching wants to be a witch - the books in the series follow her on this journey (Hat Full of Sky, Wintersmith, I Shall Wear Midnight complete the series)
The nomes (no g) are looking to move, the Bromeliad Trilogy is great fun! Diggers is the second in the series, preceded by Truckers and followed by Wings. Pratchett, as always, has created a world like no other. :)