Two lessons. The slides can be used as worksheets for the students to work though.
To be able to measure and draw straight lines. (grade 1)
To be able to the perimeter of rectangles and other polygons. (grade 2)
To be able to find the area of rectangles. (grade 2)
Students progress from counting 1cm squares, to measuring lines and sides, to calculating the area of a rectangle.
This interactive version allows students to use an on screen ruler to measure.