Frozen Lemonade Squares

INGREDIENTS:
9 graham crackers, finely crushed
1/4 cup margarine or butter, melted
1 qt. frozen vanilla yogurt, softened
6 oz. of frozen lemonade, concentrate, thawed
1/2 cup thawed Cool Whip

DIRECTIONS:
Mix graham crumbs and margarine; press onto bottom of a 9-inch square pan.
Beat yogurt and lemonade concentrate with mixer until well blended; spread over crust
Freeze for 4 hours and serve with cool whip.