I agree with Dottie. Our DS (5.10) at the time of testing on WIAT would not have had any reading scores (except for word reading). Luckily the tester used out of level testing (pretended that DS was year older) and that gave us additional reading comprehension and pseudoword decoding, at which point she could calculate the reading composite. But these are not official, although she still included the scores in her report.
WJ has timed portion of the test and higher ceilings, WIAT is untimed with lower ceilings (160).
In my DS's situation, the testing scores on WPPSI-III seem to be an underestimate, compare to scores later on SB-5 (at which point he also hit several ceilings, LOL).
