LAF is correct on the Flynn effect. I would add that the data appears to suggest that the Flynn effect is more severe with examinees further from the mean, so the score inflation due to norm obsolescence may be more than the 4 or 5 points predicted by the Flynn effect. Other relevant factors are
1) her age. At age 6, we are still looking at somewhat unstable scores. I doubt you will later find that she is Average or below, but the exact level of GT-ness may shake out differently when tested as a 9 or 10 year-old.
2) standardization group. From what I recall, your DD properly belongs on the AU/NZ norm tables, which, unfortunately, do not exist for the SB5. Research on the kind and magnitude of error resulting from using USA norms for AU/NZ examinees is mixed, but generally suggests that it is not appropriate to do so, and that the error usually inflates scores (thereby proving that Aussies are more intelligent than Americans
).
3) retest effects. Although there is not a huge retest effect going from one cognitive instrument to another, I notice from your past posts that this is her third test since age 3 (though the other two were versions of the WPPSI). Three administrations within three years does have the potential to artificially inflate scores due to practice effects, at least of the form of general familiarity with IQ tests. I would be extremely careful about having her tested again any time within the next two years, as she has now seen versions of the two major cognitive instruments (although she would most likely be tested using the WISC next time, and not the WPPSI, many of the tasks are the same, if not the exact items). You might want to "save" that assessment for when she is at least eight years old, when the scores are likely to begin to become more stable.
For many children, it's also important to consider the psychological impact on them of frequent, repeated IQ assessments, as the experience may inadvertently communicate to them that there is something wrong with them, or that they are not meeting some unspoken standard of smart-ness. Although the previous two assessments (which are subject to the same caveats about extreme youth as this one) are about 10 points lower than this test, they still show a very capable young lady.
In summary, it is likely that these scores are inflated in some way, but unclear just what the magnitude of inflation is. It is unlikely that correcting for inflation would drop her "true" score into the Average or below range, but quite possible that it would revert to the MG range in which she has twice previously scored (ETA: actually the top of the MG range, which is not all that far off of saying the beginning of the HG range), one of them as recently as this past spring. Although, then again, it may be that the SB5 captures aspects of her cognition that were not as accessible on the WPPSI.
Regardless, at this point I would base grade acceleration decisions less on her exact LOG, and more on her current academic and social-emotional needs, including the executive function demands of the potential receiving grade, and the amount of scaffolding needed and available for any gaps or delays in EF skills she might have compared to NT students in that grade. In addition to the excellent acceleration resources indigo has posted regularly elsewhere, I would repeat my parents' protocol from my childhood, which was to place children into a grade approximately one to one-and-a-half grades below their "actual" instructional challenge level, to offset the increased EF demands, and to leave enough leisure time that life out of school could be as filled with play and self-directed exploration (e.g., swinging for hours, lying on the grass looking at clouds) as it should be at that age.
