DS's first grade teacher puts him on Adapted Mind Math most days. It is similar to ixl.com but it has optional videos with some/most of the lessons (some of them stolen from Khan). They also can move through it much more quickly than ixl, in that ixl tends to drag kids through tons of questions for each skill. There are also worksheets that can be printed out from each topic. We have the password so he does it at home as well. I was shocked one day when the teacher emailed me and told me to tell him that he needs to use scratch paper because he makes too many computational errors. She was checking his account on her end.
The school paid for the subscription for all the kids in the class. We had an ixl.com subscription for a year but the kids lost interest in it after a few weeks when the novelty of the prize board wore off. They did still do it occasionally after that but it involved bribery. It's really just like online worksheets, it's not a game or particularly interesting in any way. Adapted Mind Math has cute "badges" that kids can earn, but if I didn't have Adapted Mind free from DS's school, I probably wouldn't bother paying for a subscription because Khan Academy is not much different and it's free. It doesn't seem like it's worth the extra cost for not many more features. Same with ixl. Adapted Mind might be better than Khan in terms of keeping kids on task because you can set it to adapt to the child, so the child doesn't have to choose anything. It just keeps going through topics in the correct order based on whether they are answering correctly or incorrectly until the child exits. Unfortunately DS has discovered how to switch the settings and he now picks his favorite topics rather than doing things in order.
If it came down to a choice between paying for another ixl subscription or Adapted Mind Math, i'd choose the latter. DS seems to be much more cooperative with it because it moves faster and there are optional videos. I think they are around the same cost.
DD's (age 8) school doesn't use Adapted Mind Math but she likes Khan Academy and sometimes does it at home. DS sometimes also watches the videos with her. Both of them really like the videos for some reason and DD pokes fun at the guy and makes sarcastic remarks. She goes to the grade level I tell her to go to, and pulls up a list of skills for that grade. They have to get 5 in a row correct (I think Adapted Mind is 6) before passing the skill.
