If you use SOS, you can use it again without purchasing another license. I believe it is all on the computer. I used SOS for several of my ninth graders classes this past year. I found it to be a pain for me because I keep a grade book. I would have like to have been able to simply export the grades from SOS to my gradebook on my computer, but this option was not available (or I didn't figure it out). I like Systematic Mathematics for grade 6 and up. I found my daughter understands math a whole lot better using it. (www.systemath.com)