You might want to avoid teaching them about DROP or
TRUNCATE until they have a bit more knowledge !

Strangely enough, the concept a lot of first time oracle
developers have understanding, is the concept of what a
USER is, as opposed to a SCHEMA.
eg. If you grant them all access to a number of tables, before they start, they automatically believe that the user they login with is the owner of that table. You might want to go through GRANTS and SYNONYMS with them at an early stage.