When my daughter ‘failed’ her 11+, this was in the mid 80’s though, I was disappointed because certain boys in her year ‘passed’, and I knew she did better than them in the routine school work, weekly tests and suchlike.
However, her very wise headmaster told me that although she worked hard, was a diligent pupil, no trouble to teach, boys developed later than girls, and by the time they were in their early teens, these same boys would have matured educationally, and be much brighter, if that makes sense, than my hard working girl.
And this proved to be the case. These same boys who I had written off achieved much as they grew older.