Have you tried Book Adventure?? We have used it for several years, my girls have outgrown it now, as they are all high schoolers and read on a college level. I highly recommend this site.
This one is for everyone, not just homeschoolers. The program states it is for up to grade 8, but if your child is above grade 8 in school, but below grade 8 in reading skills, I would think you would still want to use it.
Points are earned for reading and answering the comprehension questions following. My girls used to get highlights magazine as a prize from this site--subscriptions were just for a few months, but they would rotate it between the 3 of them for a full year subscription.
Check it out!