Having a free period will benefit with less missing work and stress 

 Students may be able to have down time to let their energy out that way they will be less chaotic later and more eligible for strong work ethic in fact some kids might be more calm after having a free period.   Part of the reason I say this is cause lots of students have after school activities and cant get to homework and sometimes cant even do it on weekends and have missing work because of that.  If you dont let this happen they tend to get more stressed and edgy and sometimes have to much energy for their teachers to handle resulting in their teachers getting mad and having less time to work.