Sharing a Unit with a Course
In certain circumstances, you may wish to share a unit with more than one course such that they are actually identical and will not get off pace. If you share a unit with more than one course instead of cloning it, any changes made to the unit will affect all of the shared courses and you cannot edit the courses independently. Don't say that we didn't warn you! If you must add an assessment that affects some courses but not all on a shared unit, you can leave the related scores blank for the students/courses that are exempt and it will not affect overall scores or show up on reports. Sharing a unit in this way is also part of the workflow if your course code changes mid year (see more here).
To share a unit, first edit the unit and select the Courses drop-down menu at the top. Then, check off the courses that you'd like to share the course with and click Save:
Cloning a Unit into Multiple Courses
Most of the time when you are creating new units, cloning is the right choice. Cloning creates a new copy of a unit for each class, allowing you to edit them separately (i.e. adding the dates can differ slightly if you get off pace). If there is a chance that your courses will get "off pace" and dates matter to you, you will want to create a unit once and clone it into each of your courses. To clone a unit, access the Plan tab and Edit the unit that you would like to clone.  click clone,  give it a name that references the class section you're cloning for (to help stay organized),  select the class/section you're cloning into, and  choose whether or not to includes assessments and dates (Clone Everything is the common choice):