Similar to Nexis Uni, because this is a full text database, using - and - to connect your concepts will, in most cases, result in a large number of items and many will not be relevant.
But, you can try
school* and teacher* and gun*
too many?
change the searach field from Anywhere to Anywhere but Full Text or Abstract
OR
bring the words closer together by using N/#
school* N/5 teacher* N/5 gun*