Place chicken in a 4-qt. slow cooker. In a large bowl, combine the sugar, soy sauce, vinegar, ginger, garlic and pepper. Pour over chicken. Cover and cook on low for 4-5 hours or until chicken is tender.
Remove chicken to a serving platter; keep warm. Skim fat from cooking juices; transfer to a small saucepan. Bring liquid to a boil. Combine cornstarch and water until smooth. Gradually stir into the pan. Bring to a boil; cook and stir for 2 minutes or until thickened. Serve with chicken and rice if desired.