You might google "disc-o-sit" for the bumpy cushion. HeadsUpNow.com sells them as some kind of cushion. The owner of Heads UP! homeschools two children w/ ADHD and she has a blog, a book (I recommend the book, even if you're not homeschooling), and she speaks at conferences.
The stability ball or the cushion offer proprioceptive and vestibular (and often tactile) sensory input to the child's nervous system, putting them in a position where they are able to attend and learn more easily. If you can't feel where your body is in space, your attention may be more concerned with where you are than on listening to the teacher. The stability ball or a bumpy cushion put the child and the child's body in a ACTIVE position, where balance (vestibular) and body position (proprioception)are working more like that of a typical kid. For some children who are wired a bit differently, the bouncy seat gives them what they need to attend.
The other product you could try is a T-stool. (google it.)
Sometimes, you don't know if they work or help a particular child until you try them.
Other things that have been helpful at my house:
Carol Barnier's book, "The Big What Now Book of Learning Styles" is AWESOME.
Judith Bluestone's book, "The Fabric of Autism," is about all the sensory stuff in kids w/ ADD, ADHD, PDD-NOS and autism. AWESOME. More inside info than any of Carol Stock Kranowitz's books, and Carol's really good (do you have her books, too?!)
Brain Gym may have some specific, in-the-moment exercises that help with attention -- does the teacher know about Brain Gym?
If you change your mind and want supplement info, ever, just ask. ;) E-mail me if you want the stuff I've gathered about epsom salts baths.
I have a 10 year old with autism.