Ha I remember taking an IQ test as a child, ( admittedly it's a different standard for children), because I was playing up in class and being disruptive, violent and just uncooperative and my mum in particular was convinced that it was because I was highly intelligent and being bored by the level of work.
So they had the school psychologist take a look. l have to laugh even now at the look on my mum's face when my IQ score came back around 96. Shattered some delusions I can tell you, but that score helped a great deal since there now wasn't the same amount of expectation that I would go to higher education and achieve a degree in something and then end up earning megabucks as some top.... whatever of my field.
Nowadays I largely find competence is something that come as a matter of patience and persistence. There are differences in how quickly a person picks something up of course, but most jobs can be performed with a decent level of ability if the effort is put in.