I think it is very difficult to discern innate ability because it can be so easily masked by effort. Lack of effort registers as lack of ability. Sometimes it's hard to keep making an effort when you lack ability. So are you slacking because you are lazy, or are you slacking because it's exhausting?

Sometimes you can help somebody find their smart by sparking their interest. Their smart was there all along. They just needed the right motivation to find it. They can learn all sorts of smart things as long as you relate it to kites, or Napolean, or horses, or whatever they find interesting.