I can't say either of my kids ever complained of being bored. The material in elementary school was VERY easy for my DD especially before she got put into a gifted program. Yet she STILL never complained to me of being bored. I know I've told the story 100X how her 3rd grade teacher told me that sometimes she felt like if it wasn't for my DD, she'd be wasting her time in class. She'd be asking questions and all the students are staring off or doodling and my DD was excitedly waving her hand in the air dying to answer the question. So in her case, even though the material was easy for her and she knew it, she still enjoyed the educational process, so I'm not sure I agree that that is always the problem. My DS was probably not quite so "exuberant" about education as my DD, but he STILL never complained about being bored. Now I'm sure that there WERE times both of my kids were bored.....everyone is... but they're not really complainers by nature, and they probably knew mom would have no sympathy, and .....I don't know....but they just didn't complain.
I guess perhaps different personalities handle things like boredom differently, but that wouldn't stop me from making my child study or do it. Even the spelling homework you talked about, I might have complained about it to DH, but I would have NEVER told my child I agreed. I would have been more of a "suck it up" type attitude (w/ more mom appropriate words obviously than "suck it up"

) It's all part of children learning the universe doesn't revolve around them (a concept even my older kids still haven't fully grasped) and that sometimes we have to do things we don't like or enjoy. I do agree with Swishina that you can certainly go through the material at a rate that she enjoys and speed it up if she grasps a concept easily, but that doesn't sound like the problem you're having.
Sorry that's not much help. So you''ve decided to go the home school route this fall? I hadn't heard you'd made a final decision.