Co-teachers feature was designed to increase collaboration between educators. The co-teachers have the same benefits as the teacher who created the Class: access to invite and remove students, share the Class ID, select a Question Set in the Library, and start a new Session, being also able to change the Session Settings as they wish.
Here we have an example of the possibilities a co-teacher have:
Valentin is the owner of the Class, but Maria, as a co-teacher, can also invite and remove students from it.
As a co-teacher, Maria can also start a Session and invite the Classes she co-teaches.