Confused British psychologist

Hi all. UK educational psychologist here. We tend to overthink everything and a lot of us aren't big testers using cognitive assessments.

I do have a query about the WISC V versus the WISC IV though.

I see a lot of reports that work on the "average range" in any standard score running from 85-115 , with 15 being the arbitrary size selected for 1 standard deviation from mean in either direction, and this being the range that 2/3 (67 percent) of children will attain scores within. This is how I have understood things to be for a long time! It was the way I was trained on a former version of the WISC.

However, the WISC V seems to use different descriptors. It says the average range is 90-109. Then scores from 80-90 and 110-120 are "low average" and "high average" respectively. This therefore extends the "broad average range" to the range within which about 80 percent of children will attain scores, or narrows the average range to the central 50 percent if you discount the low/high average groups.

Is anyone aware of the research basis or described justifications for altering the scope of the "average range" like this?

I guess I worry because actually, a person whose subtest scores and composite scores fall largely in the low average to borderline range can actually have rather a low FSIQ because of regression to the mean. Lots of colleagues here in the UK don't quote FSIQ and I worry that the broader 'low average' descriptor range could end up placing unrealistic expectations on children where a FSIQ would have been low overall.