#!/usr/bin/perl

use strict;
use warnings;

my %pupils = (
  'Foo 101' => { 'Bob' => 88, 'Sally' => 99 },
  'Foo 102' => { 'Jesse' => 68, 'Raphael' => 93 }
);

my $class_to_check = "Foo 102";
my @namelist;

foreach my $nm ( keys %{$pupils{$class_to_check}} ) {
  push @namelist, $nm;
}

print "Student in $class_to_check: $_\n" foreach @namelist;
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Basically you're missing a '%' in keys $pupils{$class} <sic>