I think that EF must be genetic in nature as well but I also believe that it can be improved with training, particularly absent major medical issues. I have three children who have varying EF levels despite being brought up in the same home environment. I have one who has exceptionally high EF, one with average EF which seems borderline given his other abilities but who has improved with training, and one with an obvious EF deficit that further deteriorated substantially due to subsequent medical issues.