I am always interested to hear from home schoolers in blogging. I was home schooled K-12. Overall I am extremely thankful for the experience, and would hope to be able to do the same if I were ever to have kids. I love the opportunity to personalize the learning experience.
 
Having stated that, there are several areas that have to be carefully handled. The first is social interaction. I was fairly social for a homeschooler, but a lot of my friends were also schooled at home. Just make sure you're child is involved enough outside of the home. If he's already in grade four I imagine he's developed skills to that level.
 
The other isn't particularly relevant in grade four. I also think that SATs in the States make this less of a concern for an American home schooler. To enter postsecondary after home education is less groundbreaking for Americans then us (I'm Canadian). However, as you work into grade 10 and beyond it's so important that you make sure he'll have options open upon graduation.
 
Best of luck! I hope I've encouraged you in this undertaking. Feel free to contact me if you have any questions, or whatever.