my @classrooms =
(
  {
    classname => 1,
    students  => [
                   { age => 0, fn => 0, id => 0, ln => 0 },
                   { age => 1, fn => 1, id => 1, ln => 1 },
                 ],
  },
)
;
my @classrooms;
$classrooms[0]{students}[0]{ln}
   = 0; #d3

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

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

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

$classrooms[0]{students}[1]{ln}
   = 1; #d3

$classrooms[0]{students}[1]{id}
   = 1; #d3

$classrooms[0]{students}[1]{age}
   = 1; #d3

$classrooms[0]{students}[1]{fn}
   = 1; #d3

$classrooms[0]{classname}
 = 1; #d1