I had a student who was basically performing at a 6th grade math level despite being in 11th grade. I told that student to go through Khan Academy starting from

I had a student who was basically performing at a 6th grade math level despite being in 11th grade. I told that student to go through Khan Academy starting from Pre-K all the way to 12th grade and don't continue unless they achieved mastery. That student went from the C math student, to ultimately scoring a perfect score on the SAT II Math. So I highly recommend everyone start for the absolute basics, even if it feels like a blow to the ego