Character Analysis
At the beginning of The Ambassadors, Strether remembers Chad as an immature little brat, and this is pretty much what he expects to find when he tracks the kid down in Paris. Chad totally flabbergasts Strether, though, by showing what a refined gentleman he has become.
In fact, Strether can't help but admit that Chad's transformation poses a huge challenge to everything he once thought about himself and his life in Woollett: "Chad had at any rate pulled his visitor up; he had even pulled up his admirable mother; he had absolutely, by a turn of the wrist and a jerk of the far-flung noose, pulled up, in a bunch, Woollett browsing in its pride" (4.1.41).
In other words, Strether realizes almost instantly that there's a whole big world outside of Woollett—but it takes (re)meeting Chad for him to see this. Just being around Chad makes Strether think that he is "the thing most wanted at Woollett" (4.1.20). He thinks that maybe Chad can come back with him and make Woollett a cooler place.
But Chad isn't perfect. Partway through the book, the young man totally gives into his mother's manipulations and decides that he wants to go home, telling Strether "I'd give anything to see her" (7.2.86). Where'd your backbone go, brother? It's only Strether's begging that stops Chad from following through on this ill-guided wish.
More on the imperfections; on top of his slip into mamma's-boy-ness, Chad basically lies to Strether throughout the entire book about his relationship with Madame de Vionnet. Chad is having an affair with a married woman, and even though this might not be a big deal to us if we've ever seen a Hollywood movie, it would have been enough to make a lot of readers turn against Chad in 1903.
For all his flaws, Chad is a loyal guy. He knows that he owes all of his self-improvement to Madame de Vionnet. But at the end of the book, Strether isn't sold on the idea that Chad will always stand by Madame de Vionnet, as he tells Maria Gostrey, "I don't think it will be for the money" (12.5.13)—Strether doesn't think Chad will leave Madame for his family's money, but that doesn't mean he won't leave her. After all, the woman is ten years older than him. And what'll happen, Strether wonders, when she gets old? It's sad, but we can't say for sure that Chad will stay with her instead of moving on to find a younger woman.
Chad's Timeline