Percentiles of the WJ scores, in the order you listed them:
98.6
99.4
99.6
93.7

>99.9

>99.9
>99.9
95.8
99.8
>99.9

So these range from, "he did better than 94 out of 100 other children his age would be expected to do on this task", to above "he did better than 999 out of 1000 other children his age would be expected to do." Or, in the terminology you used, "6 out of 100 children his age have this score," up to "less than 1 child out of 1000 his age scores this well."

...pronounced like the long vowel and first letter of the alphabet...