Passage comprehension on the WJ-III is really weird. The kid reads a passage with words missing and has to supply the words. You might want to ask that the WIAT be administered instead. Or even any test that uses a more normal procedure for discerning reading comprehension.

(I have a kid who started reading at age 2. He took the WJ-III at age 7 and scored at the 99th percentile for passage comprehension. Then he took it again at age 8.5 and the raw score was *below* what it was the previous time, meaning that there were fewer items correct. I *know* his comprehension had improved tremendously during that time, so obviously the test was wonky.)