Clean berries, removing over-ripe fruit for cornstarch mixture.
Stir drained berries and 1/4 C sugar in a large bowl.
Combine cornstarch, 1/2 C sugar, water and a few mushed berries in small sauce pan.
Cook over medium heat, stirring constantly until sauce thickens.
Remove from heat and pour over berries.
Stir until evenly coated and put in prepared pie shell.
Serve with Cool Whip or whipped cream.