It’s not true that law schools fail to teach trial procedure, although it’s true that it’s more of a general you-are-entitled-to rather than a specific, “Rule 4:12 allows you to move for sanctions and an order compelling if you don’t get answers to a interrogatory submitted under Rule 4:8…”
But since discovery is a matter not only of rules but of case law, it’s pretty basic. Brady v. Maryland, for example, is a seminal case - and one, I assure you, that’s taught in law school - that relates to prosecutor’s requirements to provide certain types of discovery. I’m not saying it’s unrealistic that Vinny didn’t know this – after all, he’s the good arguer who’s not a great scholar - but his law school would certainly have given him the opportunity to learn it.
All due respect to Dewey Cheatem Undhow’s characterization of the prosecutor, but the immediate move for dismissal wasn’t that realistic. After all, jeopardy had attached - who knows what sort of alibi the two other boys might have had – and even though they had a .357, there was no proof it was the murder weapon. A much more likely scenario is that he’d request an adjournment, and even offer no opposition to an unsecured bond, while they checked out the new suspects, and then offer to dismiss at a later time.
We can discuss more in-depth the ramifications of the defense remaining silent, or joining in the motion to dismiss, if you like. 
In any case, the wildly unorthodox tactics of Vinny should have given the prosecutor and the judge more pause than they did. Their neat-and-tidy murder case could well have derailed on appeal for ineffective assistance of counsel: the guy representing them had no trial experience whatsoever, was unfamiliar with the basic rules of discovery, and apparently didn’t even realize he was entitled to cross-examine witnesses at the preliminary hearing. (The latter might be viewed as a strategic choice; in this case, it was not).
In real life, serious inquiries would have been made prior to trial, and the judge would likely have, at a minimum, assigned local counsel as co-counsel, given that the lead attorney in a capital case was not licensed in the jurisdiction.
That said, the courtroom procedure was not as terrible as, say, Judging Amy or Matlock.