Creating class teams for your students is necessary when using Microsoft Teams for your classroom. As a teacher you may want to limit your student's ability to create their own teams.
To restrict students from creating new class teams, you need to work with your IT Admin to change the student's security group in Office 365 for your school. Teams is a part of Office 365, which means that an Office 365 security group set up to limit users from creating Office 365 Groups will carry over to Teams.
The specific instructions for setting up these Office 365 Group permissions are found in the topic Manage who can create Office 365 Groups.