I can't speak to the interview process but I can definitely speak to the initial application process. I have had a very professional experience with IXL but I would be wary of their job postings. From what I understand, they are simply gathering information, but are not necessarily interested in hiring at the moment.
The application was easy, and I was contacted right away for an interview. I was told that the interview would be getting to know how my experience fit the role, but instead it was a technical interview. After the interview, I was told I'd be contacted in 1-2 days but it took 2 weeks.
Interview questions [1]
Question 1
"How would you introduce this math topic to students?"
I applied online. The process took 2 weeks. I interviewed at IXL Learning in Mar 2017
Interview
While other reviewers had prepared me for an initial phone interview with a possibly outsourced, unprofessional person, I had a pleasant conversation with a young woman who worked in the department where I was applying. She was able to answer my questions about the work, which was beneficial. A couple of days after the interview, they sent me the written assignment. I know others are worried that IXL is making qualified candidates do free work for them, but they'd only get two questions to use from my completed assignment anyway. I wasn't too worried about this, but I suppose I can check back on their website to see if my material shows up in one of their skill sets! (If so, I'll report back.) Several days after I turned in my completed work, I received a fairly kind stock rejection email. "We have decided to proceed with other candidates who meet the company’s needs more closely...Thanks for your time." I have a PhD in a relevant humanities field, so I'm not sure who they think fits the needs of their company. I would be interested to know...
I applied online. I interviewed at IXL Learning (San Mateo, CA) in Jan 2017
Interview
I saw a Facebook ad for the position in November, 2016. I submitted a resume + cover letter online in late December. I heard back from a recruiter a couple of weeks later, who set up a phone interview with a team member a few days later.
The phone interview was a very introductory screening - it's not a full-fledged interview. others have said, they do a riddle, but it REALLY isn't about whaAfter that, I got a job test that tests logical thinking and some of the most basic responsibilities of the job. It really is just to see if you would like and be good at this kind of work. Despite what some people have suspected in reviews, they won't co-opt your work. If you get the job test and think that that might happen, you probably don't understand the job that well.
A couple of days after the job test, they held another phone interview with my potential supervisor to dissect the job test and ask additional questions. After that, they offered me the chance to fly down there to do an in-person final interview, but the timing didn't work and I did a Skype interview instead. The final interview was done in stages with various team members and more senior supervisors. After a reference check, I got an offer and accepted.
The process was smooth and professional. If it seem weird that they're constantly soliciting feedback on the process, that's just the way they are. You should apply if this sounds like your kind of job!