What is the metaphorical significance of "digression" in Chapter 24 of "The Catcher in the Rye"?
Holden defends Richard Kinsella, who was constantly interrupted during Oral Expression class, because he made digressions, or wandered off subject, during his speech. Holden identifies heavily with Kinsella, telling Antolini that Richard:
"Was a very nervous guy, I mean he was a very nervous guy, and his lips were always shaking whenver it was his time to make a speech and you could hardly hear him. He got a D plus because they kept yelling 'Digression' at him all the time." (Salinger)
Holden is making a point that it was the fault of the others in the class that caused Richard Kinsella to get a poor grade. If they had been patient with him, and understood how nervous he was, they would not have interrupted him so many times. Holden is also pointing out the environment that exists in high school, especially a fancy private school like Pencey Prep. There is a lot of competition between students and little or no tolerance for weak people like Richard Kinsella and Holden Caulfield.
Kinsella and Holden to a dgreee are left out by the group, marginalized and therefore they have a harder time succeeding in school.
Holden suggests in this comment that the system is against boys like Kinsella and himself, because not everyone is good at all subjects, but there are no exceptions made. Kinsella had to take Oral Expression whether he was terrified to speak in front of the group or not.