Hi @rvalburg
It is always wise to debug your code. This is the idea of dumping out the value or a variable to make sure it is what you are expecting it to bo. You can debug like so:
<?php
echo '<pre>';
print_r( get_sub_field('school-afbeelding') );
echo '</pre>';
?>
What is the value of teh sub field? Is it an array, string or an ID?
Perhaps you need to change the return type option on the image field and also read over the image field documentation to understand how these return types effect the code.
Thanks
E
