Treecritter, we did something very like that during the worst of first grade (right before we managed to swing the skip from the end of first to the beginning of third. It made a tremendous difference.
We actually only started about the end of March, so did it for about 2 and a half months and we did a day off, every two -three weeks. They were preplanned, usually in the middle of the week - something for my then DD7 to look forward to.
One thing that we had a problem with though, was that by the time we started, she was so fried on school, that we actually spent most of the first couple of days doing little or no homeschool, rather just decompressing. Other places on here, I've seen something like "about one month of unschooling to decompress from each year of bad-fit schooling". We didn't have that long, but complete decompress for 3-5 hours the first couple of days we did this was enough to generate some interest by the middle of the afternoon. By the third or fourth 'homeschool day' she generally only needed an hour or so before she was looking for 'school stuff' to do.
Good luck.
