SES

You're also just asserting SES as a cause rather than as part of a complex relationship of cause and consequence. China and South Korea were poorer than many MENA states were, nobody doubted East Asian IQ still.
And oil rich arab states dont do especially well on standardized testing, and they do spend the money on that so it isnt just being hoarded
SES also covaries with race, so it is best to use comparisons of similar SES but different races, with the infamous finding that the poorest white kids can compete with the richest black kids on the SAT (which proxies IQ well)