Teachers might put two classes together for a group project and team teach.
Example
A new teacher is having difficulty with a group, and a more experienced teacher works together on a plan for a class, and teach the class together, allowing the new teacher to gain confidence planning for the group, and to see the group with another teacher.
In the classroom
As well as the benefits for the teachers, team teaching gives learners an opportunity to be exposed to different types of language, this including accents, registers and idiomatic language. It is also an opportunity for them to try various ways of learning, as all teachers use different tools in the classroom.
Further links:
https://www.teachingenglish.org.uk/article/team-teaching-esp
https://www.teachingenglish.org.uk/blogs/davedodgson/teachers-learners-part-5-take-a-look-around-you
https://www.teachingenglish.org.uk/blogs/paulabello/clil-school-team-teaching-part-4
https://www.teachingenglish.org.uk/blogs/dario-banegas/dario-banegas-against-team-teaching