_list_header.php

<tr>
  <th class="batch checkboxes"><input type="checkbox" class="checkbox" /></th>

  <th>
    <?php echo link_to('Username', '@sf_guard_user', array('query_string' => 'sort=username&sort_direction='.$helper->toggleSortDirection('username'), 'class' => $helper->getSortDirection('username'))) ?>
  </th>

  <th>
    <?php echo link_to('First Name', '@sf_guard_user', array('query_string' => 'sort=first_name&sort_direction='.$helper->toggleSortDirection('first_name'), 'class' => $helper->getSortDirection('first_name'))) ?>
  </th>

  <th>
    <?php echo link_to('Last Name', '@sf_guard_user', array('query_string' => 'sort=last_name&sort_direction='.$helper->toggleSortDirection('last_name'), 'class' => $helper->getSortDirection('last_name'))) ?>
  </th>

  <th>
    <?php echo link_to('Email Address', '@sf_guard_user', array('query_string' => 'sort=email_address&sort_direction='.$helper->toggleSortDirection('email_address'), 'class' => $helper->getSortDirection('email_address'))) ?>
  </th>

  <th>
    <?php echo link_to('Created At', '@sf_guard_user', array('query_string' => 'sort=created_at&sort_direction='.$helper->toggleSortDirection('created_at'), 'class' => $helper->getSortDirection('created_at'))) ?>
  </th>

  <th class="actions">Actions</th>
</tr>