Order by Custom Field

Hi, I am trying to order a list of people by a custom field, whose key is sort_by.

I don’t get why this code isn’t working:

<?php
$args = array( ‘post_type’ => ‘teacher’, ‘posts_per_page’ => 30, ‘meta_key’ => ‘sort_by’, ‘order_by’ => ‘sort_by’ ,’order’=>’ASC’ );
$loop = new WP_Query( $args );
while ( $loop->have_posts() ) : $loop->the_post();
echo ‘<div class=”entry-content”><h2 class=”teachers”>’;
the_title();
echo ‘</h2>’;
the_excerpt();
echo ‘</div>’;
endwhile;
?>