The Pro version of Socrative allows you to create additional rooms. In each room, you can launch a single quiz so if you have multiple rooms, you can have multiple quizzes running at the same time! Just make sure you share the correct room name to your students. 

To create a new room, go to the Rooms header and Click 'Add Room', then enter a room name (Keep in mind room names must be unique and can be a combination of letters and/or numbers.)

Then, click Add. (If the name is not unique, you'll get an error message indicating it is not available, and you can enter a different name.)

You'll now have made a new public room. If you'd like to make it private, you can create a roster. See this article to help with creating a roster manually or import a roster.  

You can only have a maximum of 20 rooms (19 additional rooms and 1 default room). If you try to create more than 20, you'll see the error message below:

To learn more about the difference between public and private rooms, check out this link.