I'm not really sure this is correct. If you have a source please do share it.
From what I've read, the reason they have difficulty saving isn't because they weren't taught to do so but because when you constantly have to no to things you want, you use up a lot of energy, or more specifically, glucose. This in turn makes you more impulsive and less rational.
For example see: https://www.psychologicalscience.org/media/releases/2010/wan...
That being the case, I don't really like the idea of labeling poor people as being poor because of their inability to save or their own foolishness. There have also been studies that show that living in poverty actually changes your brain and makes you less intelligent.
It's a self perpetuating cycle as far as I can tell