Cross-hatching is fun, but a difficult art technique (at least in my opinion). The third/fourth grade class picked out some animals from Zoobooks magazines and drew them in pencil. Then, we looked at Brian Selznick's books for inspiration. Wonderstruck
His novels are full of beautiful cross-hatched drawings, alternating with the chapters. Plus, the two books I have read by him are charming and wonderful stories. Read them! You'll love them too, I guarantee it. They are listed below. I think bringing these types of books into the classroom is a great way to tie in to real-life applications and literature, as most of your kids will have seen these books before. If they haven't seen the books, they will probably want to read them after looking at them. I photocopy some of the pages and pass them out for the kids to look at. I also have the books available on the table for the kids to browse if they wish. Your school library might have them, but I purchased copies for my classroom.
After the kids drew their animals, I demonstrated the cross-hatching and shading for them and the kids made sure to keep their reference pictures close by.