The key teacher is his former English teacher, Mr. Antolini. Whereas Spencer encountered Holden at the beginning of his episodic adventure, Mr. Antolini finds Holden toward the end, at his most vulnerable point. The scene with Mr. Antolini is the turning point of the novel (or, rather, it should have been the turning point). Instead, it is an anti-climatic episode in which Salinger gives no easy answers.
Holden wants to be rescued by Antolini, but Salinger (who uses Antolini as his authorial voice) provides Holden with this sage advice:
"This fall I think you're riding for - it's a special kind of fall, a horrible kind. The man falling isn't permitted to feel or hear himself hit bottom. He just keeps falling and falling. The whole arrangement's designed for men who, at some time or other in their lives, were looking for something their own environment couldn't supply them with. Or they thought their own environment couldn't supply them with. So they gave up looking. They gave it up before they ever really even got started.
Antolini also says, "a foolish man dies for a cause, a noble man lives humbly for one." James Castle was that foolish man, as he saw first hand. Knowing this, Holden realizes his desire to be a teenage martyr is foolish and idealistic--a romantic pipe dream. So, Antonlini talks Holden out of sharing Castle's fate, which is to say he talks him out of suicide.
And then there's the "flit" stuff, the homosexual overtones. The way Antolini strokes Holden is both sweet and disturbing. I don't really want to debate it, but it is rather amusing how the reader thinks Antolini is going to provide Holden with the answer of all answers (which he does), and then Salinger undercuts Antolini (and himself) with the flit episode. Overall, though, I think Salinger's decision to avoid using Antolini as the Deus ex Machina is a wise one.
Here are my notes in more detail:
I. No Deux ex Machina
A. literally “God out of the machine”
B. literary definition: “a plot device or character that rescues a hopeless situation”
C. Mr. Antollini: voice of Salinger; Mr. counter-culture professional
D. has a chance to rescue Holden
E. His advice:
1. Holden is “in for a terrible fall”
2. "The mark of the immature man is that he wants to die nobly for a cause, while the mark of the mature man is that he wants to live humbly for one."
F. Salinger discredits Antolini in the end by casting him as possible gay pedophile (no rescuing; no morals)
G. Anticlimactic ending: does Holden ever grow up? "don't ever tell anybody anything. If you do, you start missing everybody" (shows regret; a downer)