So many more factors go into school acheivement than just IQ, such as motivation and family pressures. Cadaans are not as motivated to do well as these other immigrants for various reasons. These immigrant kids may be doing better but give them IQ tests and you'll see the cadaan kids come out on top as a group and u might even have some of the cadaan boys who never studied or handed in assignments and were failing their classes score the highest on the tests. Whites are more intelligent on average than blacks, Arabs, brown people, natives and South East Asians. The only people who give them competition are East Asians like the Chinese, Japanese and Koreans. But even here there is an important caveat...the East Asian IQ is about the same or maybe even slightly higher than the White IQ on average but their IQ distribution on the bell curve is more narrow. This means they they have less idiots than cadaans but also substantially less geniuses as well. That's why the greatest creatives, philosophers and minds in general usually happen to be cadaan and not East Asians.
The same pattern is observed between men and women, with the IQ of men being a few points higher but their bell curve being more spread out than the bell curve of women, which is more narrow. This means most women hover around average IQ and dont have many idiots nor highly intelligent/genius level people, while you'll find many men who are quite dull but also quite a chunk who are highly intelligent and even genius level. The only race/ethnic group which beats everyone, including cadaans and east asians, are the Ashkenazi Jews, who happen to be the most inelligent group of people in the world. Just look at each group and their achievements and it'll all make sense. Reality never lies.
All of this mind u is backed up by countless studies and experiments.
For your first line, you brought up IQ in relation to educational achievement and now you're arguing its more complex. Seems like you agree with me, more than you realize
There are big differences between "white" educational achievement in North America and the UK, for example, and the former also have immigrants. Ive posted too much today, so Ill return to this another time, but uncritically buying Bell-Curve theory arguments without questioning their assumptions requires you to discount a whole lot of factors.