9/9 or earlier problem potentially... String issue


I keep getting this error:
Traceback (most recent call last):
File "python", line 57, in <module>
File "python", line 54, in get_class_average
File "python", line 30, in get_average
TypeError: string indices must be integers, not str

for this code (numbers added in reference to above error). I am not sure where the string issue is coming from... Please help?

def get_average(student):
    homework= average(student['homework'])*.10 - Line 30
    quizzes= average(student['quizzes'])*.30
    tests= average(student['tests'])*.60
    return homework+quizzes+tests    

def get_letter_grade(score):
    if score >=90:
        return "A"
    elif score >=80:
        return "B"
    elif score >= 70:
        return "C"
    elif score >= 60:
        return "D"
            return "F"

def get_class_average(students):
    for student in students:
        results.append(get_average(student)) -line 54
    return average(results)

print get_class_average(students) -line 57
print get_letter_grade(get_class_average(students))


SOLVED HERE : http://discuss.codecademy.com/t/9-how-is-everybody-doing/3316