Great practice-Robust Data
This program is probably more liked by teachers in my school than it is by kids. It doesn't have the engaging experience of programs like Sokikom (quite a bit more expensive than iXL) or Sumdog (Quite a bit cheaper than iXL). It is somewhat similar in engagement value as Khan Academy. However, it lacks the ability to 'level' up (avatars, etc.) that students in my class really seem to enjoy.
However, the data available from iXL is extremely valuable for teachers. It is easy to track in what areas students are doing well, and in which areas they need more support and review. It is one of the interventions we use as part of our RtI program in math.
How I Use It
Students use iXL in two ways in my class. It is used primarily as part of their personalized math rotation. Based on what the student needs review (or enrichment) in, I can recommend that skill (within the grade or even flexing up or down a grade as needed). This allows for personalized and differentiated instruction.
We also use it as homework. After introducing a concept, it's a great way to have students practice what they've learned at home and provides the needed supports that some students need for review.