Reading comprehension was a huge concern when my sons were in 9th grade. I thought - and worried - about it a lot. The thing that frustrated me was that my kids would interact with the books they read (laughing at the funny parts, for example) but when it came time for "reading comprehension questions" they didn't seem to do very well. I ultimately decided that for us, having my child understand the book meant interacting with the book. I decided that reading comprehension questions weren't the best gauge of real understanding. To learn more about this idea, you might want to read Ruth Beechick's book, "You CAN Teach Your Child Successfully."
It is most important that your student is encouraged to read and write at their own level. Whether they are above or below their grade level is not nearly as significant. Once your child knows the mechanics it probably just boils down to practice. Encourage your child to write every day.
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