As the title states how did parts of Scotland turn to the feudal system? After existing within a tribal culture for so long, was the transformation gradual or did it occur under a single king, for example.
When asking questions pertaining to feudalism, it's good to check the FAQ on feudalism. There's a good explanation as to why the term is problematic.
I would add a line to your question clarifying exactly which social and economics features you mean when you say "feudal system."