Since Google Classroom is designed to facilitate a paperless classroom, there is no in-built method to easily print all the submissions for a given assignment. However- there is an easy way to do it! You can find instructions in this blog post. 

https://alicekeeler.com/2015/06/10/google-classroom-save-student-work/

If you want students to print their own they just need to open the work either from the Classroom folder in their drive or just click on the assignment within Google Classroom and then open it to Google docs / slides and print as normal.

Hope that helps :)