pages submenu with active current page

subnavigation.php

<?php global $id;
$args = array(
  'child_of' => 39,
  'sort_column' => 'menu_order',
  'post_type' => 'page',
); 
$pages = get_pages($args); ?>

<ul class="submenu">
  <?php foreach ( $pages as $page ) { ?>
  <li class="<?php if (is_page($page->ID)) echo 'current_page_item'; ?>"><a href="<?php echo get_page_link($page->ID) ?>"><?php echo $page->post_title; ?>, <?php echo $page->member_group; ?></a></li>
  <?php } ?>
  <?php wp_reset_postdata(); ?>
</ul>