In NYC, they went with the OLSAT so they could identify cheaply across the whole city. Anyone could take it, it was free -- though I do not know how well it identifies.
Anyway, the result was that there were less kids identified as "gifted" in the low socio-economic groups. Asians do the best, whether in low income groups or not though.
Use Occam's Razor. Much research has found East Asians to have an average IQ of 105, and blacks to average 85, so big "disparities" in the fractions of the two groups scoring above 130 should be expected.
