A reader (Panjoomby) commenting on the previous post asked a question about the 0.81 correlation between intelligence and scholastic attainment, commending Deary et al. for their methods, so I thought I would pick out the key part of the paper for illustrative purposes.
The authors did a factor analysis of the Cognitive Assessment Test (CAT) which is shown in the structured equation below as F1 and a factor analysis of the most commonly taken GCSE exams which is shown as F2. The correlation between the two is 0.81
This method, described in more detail in the text below is the best way to present the results. As other readers have commented, this is a very strong correlation, unusual in social science research.