G'day atu,

Welcome to the monastery.

You have some syntax errors there (e.g. my $student = (...); my $student = (...);). Use the strict and warnings pragmata to get feedback from Perl: see my code below for usage.

I'm guessing you're probably after something like this:

#!/usr/bin/env perl -l

use strict;
use warnings;

use Data::Dumper;

my @classrooms;

my @students = (
    { studentName => 'John', studentSurname => 'Something',
        studentID => 9534, age => 12 },
    { studentName => 'Mary', studentSurname => 'Something2',
        studentID => 5489, age => 13 },
);

my %classroom = ( classroomID => 10, classroomName => 'classroom1' );

push @{$classroom{students}}, @students;

push @classrooms, \%classroom;

print 'Name of 1st student in 1st classroom: ',
        $classrooms[0]{students}[0]{studentName};
 
print 'The whole school:';
print Dumper \@classrooms;
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Output:

Name of 1st student in 1st classroom: John
The whole school:
$VAR1 = [
          {
            'classroomName' => 'classroom1',
            'students' => [
                            {
                              'studentSurname' => 'Something',
                              'studentID' => 9534,
                              'studentName' => 'John',
                              'age' => 12
                            },
                            {
                              'studentSurname' => 'Something2',
                              'studentID' => 5489,
                              'age' => 13,
                              'studentName' => 'Mary'
                            }
                          ],
            'classroomID' => 10
          }
        ];
[download]

I'd recommend you look at "perldsc - Perl Data Structures Cookbook" which describes these types of structures in detail.