Our whole county uses it from kindergarten right on up to 8th grade. This will be our third year I think. It's a pain in the @$$ and the kids generally hate it. We have BOY, MOY, and EOY scores listed on report cards and expected benchmarks.
The program can only be "played" on a PC because it needs flash to run. When the kids assess for the first time, most of them don't even know what in the world to do with the mouse. They usually only know to touch a screen (I love the ones who are rubbing and banging the mice on the monitors).
When they get a certain number of questions incorrect during an assessment they get sent to a quick game. It's like a brain break. As soon as the first kid gets a game you know it. All heck breaks loose and kids are crying and fretting wondering why they don't have a game. The game literally only lasts about 27 seconds and then the kid is back to answering questions. Then that kid starts crying.
There are lots of ways to monitor progress and differentiate instruction with the program, but it just seems like way too much screen time to me. During literacy and math stations our kids are expected to log on and work on their iReady lessons. They are "required" to have 45 minutes lesson time of both math and reading per week.
The funniest part is when I log in to see what they've been doing. There are kids who, no lie, have like an hour and a half of logged in time. Then there are most kids who have been on for 7 minutes all week in math and reading combined!

what in world were you doing kid? I'd rather a kid be doing almost anything else in my room than staring blankly at a talking cartoon.