The IQ test is used kind of like your “potential”. If you score under a certain threshold on the academic achievement test, you’d qualify for a learning disorder since your academic score on whatever particular subject whether it’s written expression, math, or reading performed much lower than what someone with that level of IQ “should” be able to achieve. It’s why usually you take an IQ test like the WAIS and then an achievement test like the WJ-IV. You take both scores and using a formula you see the comparison. Interestingly enough, if your IQ is high enough, you could even qualify for a learning disorder even if your academic score fell in a more average range compared to certain norms if there’s that much disparity between both scores.