Not to put too finer point on it 3 out of 4 of my biological grandparents and both parents were not blessed academically. I was very bright at school and it came really easily to me. DH was also bright but had to work at it more than me.
DS1 - doing okay, could do better but prefers making things to writing and maths.
DD - exceptionally bright at everything, loves school, loves learning, it all comes really easily to her.
DS2 - still small so not so easy to tell but at least average in some things and above in others.
Is intelligence genetic in any way, is it just coincidence or down to the individual child's liking or not of school?