Pencils and erasers: And lots of 'em.
Colored pencils, markers, highlighters, pens: The requirements for writing tools will be different than they were for elementary school, so check with the school to make sure you get what your kid needs.
Blank CDs or a flash drive: Yep, school has gone digital and your kid is likely to need a way to transport that report from the home computer to the school one.
Poster board, glue, tape, ruler, scissors, tape, clear report covers: All the makings of a school project or report. You can keep all of this at home.
Pencil sharpeners: One for the pencil case, one for at home.
Pencil case or box: The ones that fit in three-ring binders are great for middle school.
Three-ring Binder: Middle school ups the ante on organization (not a strength for the puberty crowd), so get a binder with several dividers to help your kid keep it all straight.
Homework planner: There are lots of electronic versions that kids find appealing, but an old-fashioned paper organizer does the trick just as well (and you won't be as upset if he loses it).
Clothes: You remember how awesome it was to have great, brand spanking new back-to-school clothes, right? Don't forget to check their inventory of socks and underwear.
Sneakers: For gym class.
Spiral notebooks: You're probably going to need a lot. Check to see if the school has recommendations on how many.
Paper: Computer, lined, graph, unlined—your kid will need it all!
Poster board: For projects and reports.
Calculator: Many middle schoolers need a graphing calculator. Check with your kid's teacher before you buy.
Stapler: Keep it at home for stapling homework and reports.
Kids' paperback dictionary: Dictionary skills are big in elementary school. So is spelling!
Computer: A laptop probably isn't necessary just yet, but a home computer (with Internet access) can be a huge boost for research. If you don't have one at home, check your local library and post their computer room hours on the fridge.
Index cards: Helpful (and usually required) for note-taking and research.
Printer and ink cartridges: If you can afford a printer, it'll save you trips to the copy shop. Buy a bunch of cartridges, because you always seem to run out when you need it most and all the stores are closed.
Combination lock: Check with the school, because your kid may need more than one for his locker and his gym locker.
A ruler: One with both inches and centimeters.
Clipboard: Great for doing homework on the bus or at the soccer game.