Hello all,
In 2015 my daughter, then 10, was tested for giftedness with the WISC-V. Her scores were:
FSIQ 129
GAI 134
VERBAL COMPREHENSION 142
VISUAL SPATIAL 105
FLUID REASONING 131
WORKING MEMORY 110
PROCESSING SPEED 89 (called her "personal weakness")

We had recently moved to the US from another country where she had attended school in that language and culture. It was felt at the time that she might have had even higher scores without the cultural differences, even though she is bi-lingual. Her Woodcock-Johnson scores also reflected the recent school/cultural change and were not reflective of her knowledge. So, the school denied admitting her to the gifted program.
She continued to be bored and dissatified with school.
We had her re-evaluted about a year later and her W-J scores were much higher. After she produced an exceptional research project they finally admitted her to the gifted program. However, there was really little differentiation or support in the regular classroom and nothing much happened in the gifted time 2-3 hours per week. Her disengagement continued to grow, culminating with her refusal this year to attend school. She homeschooled this year. She has always tested in the 98th/99th percentiles on the MAP tests.
She is now entering high school and I decided to have some testing done to try to address her disengagement and other issues.
She was tested with the Stanford-Binet with the following results:
FSIQ 109
NONVERBAL IQ 100
VERBAL IQ 117
ABBREV IQ 106
FLUID REASONING 109
KNOWLEDGE 120
QUANT.REASONING 103
VISUAL SPATIAL 111
WORKING MEMORY 97

Needless to say I was astonished at the lower numbers. The test administrator kept trying to convince me that the two test scores were "equivalent". I understand that the different test favor different apptitudes, but I cannot see how the two test scores can be equivalent. Can anyone advise about this?

Additionally, recently she participated in a research study with IQ testing as part of it and scored the following on the WASI-II:
VERBAL IQ 116
PERFORMANCE IQ 128
FSIQ 125

In this case it's strange that her verbal was lower when it has always been her great strength. The other two are a bit lower than the original WISC but generally in line. The fact that she had done this in the research study was the reason she was given the Stanford-Binet.

All thoughts appreciated.

Unfortunately, this is common in US public schools since the introduction of Common Core and the change to rating/ranking teachers and schools based on reporting equal outcomes for all students; this often involves capping the growth of students at the top.

Measuring IQ is not an exact science like measuring physical elements such as height and weight. Although the scores of various test instruments differ (as summarized on this Hoagies page), each test would indicate the percentile (percent of the population above which the test taker scored).

I'm linking to a recent thread, The story of an unidentified GT child, which I found inspirational and thought you might, too: opportunities can be found to challenge one's self, outside of a gifted program in school.

Welcome!

As indigo notes, cognitive assessment is not an exact science. It is, however, usually somewhat stable when obtained under reasonably standard conditions. A few notes, though: the structure of the three tests you described is not the same, so the only really comparable measure is the global measures (FSIQ), which are actually quite similar between the earlier WISC-V and the more recent WASI-2. Both of those instruments are in the Wechsler family, and thus more comparable than either is to the SB5. The SB5 has a very different design, where the VIQ and NVIQ each include measures that cut across the WISC-V VC, VSI, FR, and WM indices, and the five factor composites are composed of both verbal and nonverbal measures. This can make it quite challenging to have any kind of coherent comparison between the SB and the Wechslers.

The WASI-2 PIQ is more akin in design to the old WISC-IV PRI, and to the current WAIS-IV PRI, which both mix measures considered VSI and FRI on the WISC-V. Even without factoring in that mixture, the recent WASI-2 PIQ is pretty much identical to the old WISC-V FRI.

So the most notable difference is the drop in VCI from the WISC-V to the WASI-2. At this point, any explanation for this would be rather speculative, but FWIW, I'll offer some of that speculation:

Over the course of four years, quite a lot of influences could have lowered her normative standing, including prolonged disengagement in her own education, which may, for some learners, mean that they are immersing themselves less frequently in challenging text, which can limit growth in vocabulary and higher-level language development.

There are also, of course, the always-possible effects of regression to the mean, where a second measurement of any extreme result would be expected to become less extreme.

Another possibility is that the original postulation that her VCI was an underestimate due to the difference between her experience as a bilingual learner in another country was mistaken; it is not impossible that her education in that previous educational system gave her a higher level of verbal achievement than that obtained by an hypothetical cognitive peer operating in the US educational environment, resulting in artifactually high VCI scores. After four years of (I guess you'd have to say inferior) US education, the inflationary effects of international education have worn off, and this then might be imagined to be her "true" VCI.

Keep in mind that, in all of these scenarios, regardless of the "true" numbers, she is still a very intelligent and capable young person, with outlier instructional needs.