Having problems getting the pager to display

I followed the instructions at http://drupal.org/node/492552 on adding pagers. However, the pager does not show on the page and a var_dump() of the output of theme_pager() shows NULL. There is enough content to have the pager show (29 rows are returned by query in $sql). Below is the code that generates the content:

  $perpagecount = 15; // How many items to display per page
  
  // The header has to be defined first to get sorting to work correctly!!!
  $header = array(
    array('data' => 'Name', 'field' => 'name', 'sort' => 'asc'),
    array('data' => 'Present', 'field' => 'occurrences', 'sort' => 'asc'),
  );
  
  $sql = 'SELECT `uid`, `name`, count(*) as occurrences FROM {users} INNER JOIN {content_field_present} ON {users.uid} = {content_field_present}.field_present_uid GROUP BY `uid`, `name`';
  $pager_sql = 'SELECT count(DISTINCT `uid`) FROM {users} INNER JOIN {content_field_present} ON {users.uid} = {content_field_present}.field_present_uid';

  // Make it sortable.  I love it when Drupal does stuff for you... <3
  $sql .= tablesort_sql($header);
  $result = pager_query($sql, $perpagecount, NULL, $pager_sql);
  // The key in the $users array is the uid, the value is an array with the
  // username and the number of times that person is present.
  $users = array();
  while($item = db_fetch_array($result)) {
    $users[$item['uid']] = array(
      'name' => $item['name'],
      'presence' => $item['occurrences'],
    );
  }
  
  $data = array();
  foreach($users as $uid => $user) {
    array_push($data, array(
      '<a href="/atrium/user/' . $uid . '">' . $user['name'] . '</a>',
      '<a href="http://officers.ridgehabitat.com/atrium/officers/attendance?field_type_value_many_to_one_op=or&field_type_value_many_to_one=All&field_present_uid_op=and&field_present_uid[]=' . $uid . '">' . $user['presence'] . '</a>',
      ));
  }
  
  $table = theme_table($header, $data);
  $pager = theme_pager();
  echo $table . $pager;