It's important to realize that there is a difference between memory and IQ. Likewise, there is a difference in the ability to generalize skills to a new situation and IQ.
I have a child with a fairly high IQ (high 120's). Yet, he has severe learning disabilities. His reasoning and thinking ability is very very strong. (measured by the WISC in the VCI and PRI) This is what most people often think of as intellectual horsepower. While his memory is also strong by most measures, he processes very slowly and has a hard time applying skills to novel situations. Things like plurals, verb tense would throw him for a loop.
Be careful about underestimating the intelligence of your students by assuming their ability to learn and apply skills related to writing mechanics is an indication of their smarts.
"IQ" is a combination of a variety of cognitive skills and attributes. And while a traditional IQ test often predicts "learning ability" and "school success", it does not do so with certainty.
