Wyldkat -
My DD9, who has SPD and also is extremely anxious (not formally diagnosed but it is obvious and has a lot to do with the SPD), CAN NOT STAND WORKSHEETS. Most of it is the repetition.
I have a very good friend who has homeschooled her two boys - one is graduating next year. She said, "Look, if they can do two math problems well, why should I make them do 10 more?" Granted Bear is fine in math but it applies to all subjects. Sometimes it is the repetition that comes with the worksheets that makes them a little nutty with us. So, I have learned to do smaller lessons where I need to and make them longer when the energy and concentration is there.
For reading, we used Teach Your child to read in 100 easy lessons. I didn't do it following the instructions to the letter (I rarely do that with anything) but it might be worth checking out. We spent a long time on some of the ending lessons but that is the beauty of homeschooling.
I would encourage you to go with his interests and try to work in handwriting with it if that is what you are working on. My daughter still doesn't like to write but she'll type 2 pages without thinking about it. I found a fun book that has riddles and jokes and she works on that - I make her do a little each day - it isn't a ton but it is enough to build her up and I've seen much more improvement in making her do a little well each day than a whole page of stuff that she zones out on after that first part, anyway.
At a young age, I would do things like have her copy sentences out of a book that she enjoys (still do that every once in a while) or just simply work on her name and address until those come well. We always joke that my husband rarely writes anything except checks and signing his name.
All this being said, I take it you have a set program which may be part of the frustration for you. I guess I'm not helping much in that case but I wanted to let you know that you are not alone. Yes, it is horribly frustrating (especially when you put out money and spend hours researching "the best" curriculum) to find out your child has no interest in a curriculum. As someone very wise has told me, "The best thing we can do for our kids is to not let them lose their love of learning."
This is different for every child and finding that perfect motivator can take a looong time and then once you get in a groove, it all changes again (ugh!). It IS worth it, if your sanity can take it. I have found the more I relax, the more she learns, but that may not apply to all children.
Best of luck! You can do it no matter what your path is ahead for Bear. Be patient with Bear. Be patient with yourself. Some days with SPD, we simply don't do what is planned b/c the senses are on overdrive (today, in my house). It is okay. The world won't end and learning how to deal with the SPD well can be a full-time job.
Take deep breaths and try to smile.
