When writing a lesson or unit plan, a teacher should state the purpose and the aims of the plan.
The purpose(s) is / are why the unit is being taught.
The aims are specific outcomes which the teacher should be able to measure by testing the students.
Example 1 - Money Math. (grade 2)
Purpose - This unit will teach students the mathematic skills they need to manage money in everyday life.
Aims - By the end of this unit, students will be able to:
Example 2 - The seasons ( K).
Purpose - This unit will teach students about the four seasons.
I hope this helps. please reply if you need further clarification.