Drupal 7: hook_menu not working correctly
Try this:

function page_arg_menu() {
  $items = array();

  $items['flashcards'] = array(
    'title' =&gt; 'Flashcards',
    'page callback' =&gt; 'page_arg_callback',
    'access arguments' =&gt; array('access content'),
    'type' =&gt; MENU_CALLBACK,
  );

  return $items;
}

function page_arg_callback() {
  // Do stuff
  return theme('page_arg');
}

function page_arg_theme($existing, $type, $theme, $path) {
  return array(
    'page_arg' =&gt; array(
      'template' =&gt; 'page-arg',
      'path' =&gt; drupal_get_path('module', 'page_arg') . '/theme/templates',
    ),
  );
}


Create a file page-arg.tpl.php and put it in /theme/templates in your module (page_arg) directory.