sorting a column in a PHP array

I am trying to sort by a column(s) in the following data structure that I have built like this:

 $counter = 1;
 $entity_list = array();

 foreach($result as $rec){
   $entity_list[$counter]['student_first_name'] = $rec->firstname;
   $entity_list[$counter]['student_last_name'] = $rec->lastname;
   $entity_list[$counter]['course_name'] = $rec->fullname;
   .
   .
   $counter++;
 }//end foreach

This is a var_dump of the $entity_list data structure.

array (size=150)     
  1 => 
  array (size=3)
    'student_first_name' => string 'Jane' (length=6)
    'student_last_name' => string 'Smith' (length=7)
    'course_name' => string 'Algebra 1A-MOD' (length=14)

  2 => 
  array (size=3)
    'student_first_name' => string 'Fred' (length=6)
    'student_last_name' => string 'Jones' (length=7)
    'course_name' => string 'Algebra 1A-MOD' (length=14)
   .
   .
   .

How do I use asort() or ksort() on this structure? I think i should be using ksort(), as it works on a key. I have tried ksort($entity_list,'student_last_name'), or asort($entity_list,'current_grade') for example.

Thank you.

You can use uasort

uasort($entity_list, 'mySort');

function mySort($a, $b) {
    return ($a['student_last_name'] <==> $b['student_last_name']);
}

But if your data come from a DB, it would be a lot easier and lighter to ORDER BY.