Pencey Prep,. according to Holden, is always advertised as being a sophisticated educational institution which maintains high academic standards and caters to elitist sporting pursuits. Holden shoots this down immediately:
They advertise in about a thousand magazines, always showing some hot-shot guy on a horse jumping over a fence. Like as if all you ever did at Pencey was play polo all the time. I never even once saw a horse anywhere near the place. (chapter 1)
Holden is quick to point out the discrepancy between the adverts and the reality of Pencey as he has experienced it. He particularly takes issue with Pencey's claim that it moulds its students 'into splendid, clear-thinking young men' (chapter 1). Holden is full of derision; according to him there are only about a couple of students at Pencey who are like that, 'and they probably came to Pencey that way,' he adds scathingly (chapter 1).
Holden, then, demolishes Pencey's glowing public image. He gives us a very different picture of a school with indifferent teachers, sordid activities, and unpleasant characters like his roommate Stradlater and Robert Ackley next door.
Of course, we can note that Holden's is hardly an unbiased judgement; the fact that he is being expelled from Pencey naturally colours his view of it.