You can announce some of your lessons as public lessons on your calendar. A public lesson could be used as an open opportunity to attract new students. You can offer open or public lesson near the exam times so that your students can attend and ask their questions without any previous appointments.
When you make a class a public lesson on your calendar, then when your students refer to your blog and look at your calendar, you will be able to enter your running public lesson as long as they know the passkey. If you wish your public classes to be entered by everyone you should announce the passkey as a note at the gate of your public classes.