David Chapman quotes Kegan a lot in his "Meaningness" blog. I included one link, but you should find more of his writing linked from there. Check out the rest of the site as well.
ETA: From the (Stanford) article this thread is attached to...
> Kegan (Robert) introduced his theory of self-evolution in 1982 in his book, The Evolving Self. In his later book, In over Our Heads: The Mental Demands of Modern Life (1994), he presented a revised version of his theory and further discussion of the implications of his work for society.
Of those two books, The Evolving Self is the easier read. I would start with that one.
https://meaningness.com/metablog/stem-fluidity-bridge
ETA: From the (Stanford) article this thread is attached to...
> Kegan (Robert) introduced his theory of self-evolution in 1982 in his book, The Evolving Self. In his later book, In over Our Heads: The Mental Demands of Modern Life (1994), he presented a revised version of his theory and further discussion of the implications of his work for society.
Of those two books, The Evolving Self is the easier read. I would start with that one.