WP_User_Query not returning users with meta – what am I missing?

Try using Subscriber, with capital S.

$args = array( 
    'role' => 'Subscriber',
    'meta_key'    => 'school',
    'meta_value'  => $school
);

🙂

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)