Software for Special Needs Classroom

Hi. I am a special ed teacher in San Diego CA. My class is unique where i have moderate to severe students that range from 5 to 10 years of age. It is hard to keep up with curriculum that meets the levels of all of my students. I would like to have IXL software which helps me to assess and assign skills that are customized to the student. I used it when I was teaching at a high school last year. The elementary school do not use it but I believe that I have a special circumstance. I only have up to 12 students. I can have a full 4 subject package for $599 per year. Anything helps. Thank you in advance.