I was taught birth order effects in middle school in the 2000's in the US in a "health" class (in the same unit we also did handwriting analysis). We were literally shown a video of a family in which everyone explained why they were the rebel as the second child, the overachiever as the first child, the spoiled brat as the youngest, etc. Birth order effects might exist... but even if that were true we should not teach them to middle-schoolers as determining their life. This is for the same reason that we would not want a video of a "typical community" showing a white male doctor, a white female kindergarten teacher, and a black male janitor even if all of those occupations are statistically more likely to be held by those demographics than the others. Because we live in a time and a place where children get to choose that they are not like their statistical cohort if they put their mind to it.

The only positive thing I took out of that class was the number of other students going "this is bullshit, I'm a first child and am the rebel of the family" or whatever. And it was a good introduction to not trusting authority.