KABC2 practice effect

While reading about the PASS theory I ran into this information, in chapter one in:

Kaufman, A. S., Lichtenberger, E. O., Fletcher-Janzen, E., & Kaufman, N. L. (2005). Essentials of KABC-II assessment (Vol. 94). John Wiley & Sons.‏

The practice effect is the amount a child's score increases from first testing to second.  The data in the case of the KABC2, refers to re-testing intervals   ranging from 12 to 56 days with a mean of 27 days.  The WISC3 data refers, as far as I can tell, to re-testing intervals of up to a few months.

KABC2:

The largest practice effects  were about 14–15 points for the Learning/Glr scale at ages 7–18. The authors argue that large gains on this scale are not surprising given that the nature of the tasks demands that children learn new material, so if children are tested again once they have learned the material, they have a distinct advantage over the first time they were tested. Indeed, the practice effect of about 1 SD over a month’s time strongly suggests

that the children really learned the material in the first place and are reflecting a certain amount of retention over time.  I'll  add, that children not only learn new material, but also find strategies for solving the test's problems.  These strategies help them the second time around. 

At ages 7–18, Planning/Gf also had a relatively large practice effect (10–11

points), whereas Simultaneous/Gv showed a moderate effect (7–9 points), and both Sequential/Gsm (–1 to 1 point) and Knowledge/Gc (3 to 3.5 points) had small effects.

What can we very cautiously learn from this information?

We learn about the "artificial" gap formed between children coming from nurturing homes and children coming from homes that are less nurturing.  Children raised in nurturing homes get more opportunities than children raised in homes that are less nurturing to perform similar tasks to the ones tested in the KABC2 tests.   Thus the scores that a child from a nurturing home gets consists of his abilities and his nurturance.  Scores that a child from a home that is less nurturing gets reflect more of his "clean" cognitive abilities.  That's why we can always be more optimistic about children from homes that are less nurturing, because the nurturance we can give to these children via the educational system can improve their performance not only on IQ tests, but in many similar academic tasks.

It's interesting that the practice effect is stronger in nonverbal tests.  These tests may have more new elements.  It's possible, that practicing with similar tasks can introduce the child to a variety of tasks, decrease the sense of novelty, and help him find strategies that will help with IQ tasks.

On the WISC-III, Performance IQ gains averaged 12.5 points as a result of retesting, as opposed to 2.5 points for Verbal IQ.

At ages 3–5, practice effects for all scales of the KABC2 tended to be small to moderate (2–6 points).   Largest practice effects were on Learning/Glr and Simultaneous/Gv (5–6 points), and smallest effects were on Sequential/Gsm and Knowledge/Gc (2–4 points).

Overall practice effects on the FCI and MPI scores of KABC2 were 10–11 points for ages 7–18 and 5–6 points for ages 3–5.