Treecritter, if the teacher is not that bad, try homeschooling by proxy by sending him with appropriate level work from home in a nice binder, divided into whatever sections the other kids do so the teacher just has to pull them out and hand them over. We did that when we tried pre-K (in a gifted school) and even having advanced puzzles and mazes made my dd a little happier (she only lasted 3 mos though, but that's another story). I would just get a subscription for edhelper.com and you can print worksheets, puzzles, and even comprehension/discussion questions for the books he's reading and it's only about $25 a year. They even come with correct answers to reduce the teacher's workload if that's a further concern.
