incas scores in tests for Primary Education how accurate are they?

[NeverKnowinglyUnderstood]

have had some test results for my son and they have suggested that the Knowledge/non verbal reasoning is a sign of potential
is correct??

The developed ability test in INCAS is the indicator of potential.

I personally find that the ages that the tests spit out are not very accurate, however the ranking of the children relative to each other is, and the progress made year on year. e.g. it may say child X has a maths age of 8 yrs 3 months, which I think is too high, but the next year it has gone up to 9 yrs 3 months, which again is too high, but does show the year's progress that the child made.