Beginner Python: Codecademy and Efficiency

• In the function get_letter_grade you were checking more conditions then necessary. Try to follow the logical difference between your function and my code. It is simple math which I used to optimize it. Also structuring it as an if-elif-...-else is better for readability.
• In get_average and get_class_average I use a thing called list comprehension. A simple google search will tell you what it is and why it is better. Google it in python tutorials if you have problem.

Edited Functions

def average(values):
    return sum(values) / len(values)

def get_average(student):
    keys = ['homework', 'quizzes', 'tests']
    factors = [0.1, 0.3, 0.6]
    return sum([ average(student[key]) * factor for key, factor in zip(keys, factors)])

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"
    else:
        return "F"

def get_class_average(classlist):
    return average([get_average(student) for student in classlist])

get_class_average(classlist)

Defining an average function (based on this), you could have things slightly clearer :

def average_list(l)
    return sum(l) / float(len(l))

def average_student(student):
    average_homework = average_list(student["homework"])
    average_quizzes =  average_list(student["quizzes"])
    average_tests =    average_list(student["tests"])
    average_total = average_homework * 0.1 + average_quizzes * 0.3 + average_tests * 0.6
    return average_total

def class_average(students):
    return average_list([average_student(s) for s in students])

In average_student, you're manually iterating over the keys in a dictionary, and you've hardcoded the weights of the various parts. What if you want to add a "presentation" component to the grade? You've got a lot of places to touch.

Consider exporting the hardcoded information into its own dictionary, and iterating over the keys in that dictionary:

weights = {
    "homework": 0.1,
    "quizzes": 0.3,
    "tests": 0.6
}

def get_average(student):
    return sum(average(student[section]) * weights[section] for section in weights)

def average(x):
    return sum(x)/len(x)

In terms of learning Python, I'd definitely agree with your instinct -- you should keep trying to make your code as clean as possible even while completing exercises. When you're learning fundamentals, it's that much more important to understand good structure.