This study (with more than a thousand citations) of 70,000 school children in the UK measured IQ at age 11 and compared with educational outcome (GCSE; standardized tests) at age 16. The correlation was 0.8.
Deary, I., Strand, S., Smith, P., Fernandes, C. (2007). Intelligence and Educational Achievement. Intelligence
https://www.sciencedirect.com/science/article/abs/pii/S01602...
I'd also argue that it's plain common knowledge. If you ask 100 people on the street, "Do clever kids have an easier time in school?", I think the answer would be a resounding yes.
Sure, there is a lot of "junk education" out there. Schools that will accept anyone, and give everyone good grades regardless of performance. That's why I wrote "at least it used to be". But Western educational systems hasn't yet regressed to a level where it's all trash.