0.8 correlation with adult height for boys aged 4, according to [0]. The real study [1] is paywalled but looks legit. I'm guessing it's even higher at age 12, though it might be confounded by puberty soon after.

[0] https://www.theatlantic.com/ideas/archive/2020/02/can-you-pr...

[1] https://pubmed.ncbi.nlm.nih.gov/21767107/