Repeating a sequence of words at the beginning of a phrase is called 'Anaphora' in rhetoric. It is used in speeches to give emphasis to the point being discussed. Thus, the speaker wanted to emphasize his point and encourage his listeners to do something as well.
A comma should be placed after "grade": Kari and Misha, who have known each other since first <u>grade,</u> are both yearbook editors and photographers.
