Students from the entire grade are divided into groups

In many schools all students from all classes in the same grade are often divided into groups according their level in particular subject (e.g. language, or math, ...). These lessons then take place at the same time.

Lets take the case, when all students from the 5th grade are divided into three language groups - Beginners, Intermediate, and Advanced on their English lessons. Obviously each group is taught by the different teacher and is placed in the different classroom.
You can solve this in the way:
1. create the division in one class: Divisions
2. copy this division into all other classes in the 5th grade: How can I copy division from one class to another classes
3. create 3 joined lessons for all groups in the same level: How to specify lessons where students are joined from two classes?

That's all. Once you add all your other lessons (input all data first), these lessons will be placed at the same time (or you can use relations for assuring this to happen).