The article does cover the fact that children who are more attractive are given more attention, and that teachers pay more attention to those children, which may very well explain the effect.
1. How much of intelligence is inherited? I am not up to date on this, but I remember that researchers don't have a consensus on this. Also, once you are an adult does G get fixed?
2. Teachers also pay more attention to intelligent, hardworking and industrious students.
Also, grown up intelligent people are usually better at taking care of themselves and end up looking better than others. Of course, this is just one factor.
Simply put, babies fixate on more symmetrical faces. It is not difficult to deduce that teachers would give more attention to more attractive students, all else being equal.
