my $classss = {
  classroom => {
    students => [
      { age => 0, fn => 0, id => 0, ln => 0 },
      { age => 1, fn => 1, id => 1, ln => 1 },
    ],
  },
};

##</code><code>##

my %classrooms;
$classrooms{classroom}{students}[0]{ln}
   = 0; #d3

$classrooms{classroom}{students}[0]{id}
   = 0; #d3

$classrooms{classroom}{students}[0]{age}
   = 0; #d3

$classrooms{classroom}{students}[0]{fn}
   = 0; #d3

$classrooms{classroom}{students}[1]{ln}
   = 1; #d3

$classrooms{classroom}{students}[1]{id}
   = 1; #d3

$classrooms{classroom}{students}[1]{age}
   = 1; #d3

$classrooms{classroom}{students}[1]{fn}
   = 1; #d3