Okay, spoilers for the book for those who haven’t read it yet:
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The big surprise at the end is that Daddy Long legs is also Mr. Jervis, the uncle of one of her room-mates. This enables to clear up the mis-understanding where Judy first rejects Jervis for some reaons, while he thinks she doesn’t love him.
However, this knowledge puts the beginning of the novel in a different light - maybe only to a cynical person of today, where stalking is no longer considered romantic?
We only see things through Judys eyes (with the exception of the first chapter), so the motivations of both the college dorm assignment and of Jarvis remain hidden to us. Still, at the beginning Judy gets her own room - she speculates because she’s an orphan, so “normal” girls don’t want to stay with her. The reader starts liking her from the very first letters for her naivity and boldness in adressing authority figures, including Daddy Long Legs himself, but also her insight and the joy of her discovery of books and “normal” life.
Jarvis meets her later, coming to meet her room-mate, his niece, but becoming more interested in Judy.
So: did Jarvis arrange that meeting because her letters to him as Daddy Longlegs had intrigued him and got him interested? Was, in other words, everything manipulated by him, including her two room-mates, one of which a relative as “innocous” pretext?
Or did he pay little attention to her letters at first and fell in love only due to the honestly accidental meeting? Did he honestly intend to visit his boring niece, although he generally didn’t like that boring side of his family and kept far away (as Judy later observed when she visited that part of the family with her room-mate)?
We do know, or can infer safely, that he later uses his position as Daddy Long-Legs to advance his cause as Jervis, once, when he forbids her to visit her friend Sally McBride at camp because of potential Jimmy as rival there, ordering her instead to the farm where he happens to show up; and again, when he tries (but fails) to forbid her a summer teaching job, because he wanted to travel to Europe with her.
So how much did he set up? Did the author intend to portray Jarvis as arranging things from the very beginning because stalking was romantic in those times? Did she intend to leave it ambigious instead?
Would for example the college administration on a women’s college in those times have bowed to requests from sponsors on how to pair freshmen; would it have been entirely alphabetical (Abbott, McBride, Pendleton?); some character or grade assessment by the teachers; arbitrary?
So, wikipedia and other cursory sources haven’t given me the necessary background, maybe some Dopers with more knowledge can give additional background?