By default, all new student posts and comments require teacher approval before they are shared with parents or posted on your blog. You can delete an inappropriate item from the approval queue and then have a conversation with the student.
In Class Code Shared Sign in mode, unapproved items do appear in the student's own journal. This is so students can see feedback left on their work by their teacher and do things like make edits and resubmit work. However, all new student items and comments still require teacher approval before they appear in the Class Feed.
As with any tool that gives students freedom, we recommend setting the appropriate expectations with students. Use this Classroom Expectations template as a guide for your own classroom expectations.