Well, it very much depends on your data structure.  But, I'm going to make some assumptions here.  Mostly, I'm going to assume that you have some kind of Status field, with values like "Completed", "Overdue", and "Due".

Now, do you want to use the Completed classes in the report (say, in a chart, or in some sort of total in the footer)?  If so, you want to do a conditional suppress on the details.

Go into the Section Expert
Click on Details
Look for "Suppress (No Drill Down)" on the right side
Click the button next to it that looks like "x-2"
This creates a formula for the conditional suppression.  If the expression you enter here is true, the section is suppressed.  If not, then the section is shown.
Enter something like: {Status} = "Completed"
Click Save and Close

Now, this should hide any class that has been completed.


If you want to exclude the completed classes from the report altogether, then you want to use the Select Expert.  This allows you to restrict what records are returned in the report.

Go to Select Expert
Assuming you haven't done this before, you'll be prompted to choose a field.  Choose Status.
In the dropdown, choose "is not equal to"
In the field that appears, put "Completed"