Instructions are from older model or another model. They are not clear, do not tell you where to use narrower or wider parts. I had two attempts before figuring out that knee rest is wide and seat is narrower. Once this was established it got done quickly, but by then I had almost fully assembled it twice.
There some sort of flaw with it as my son still has hunched back while using this chair, so it doesn't deliver the desires result. Got it to improve his posture.