From the beginning of the series towards the end, you basically see the activities these girls do on a day to day basis. You see how they socialise and what events they enjoy doing. As you get to know what they like to do, you will start to get to know more about their personalities and maybe relate to one them when you were younger or as of now. Their personalities is so common to the average 3rd grader in the real world, it's not too hard to fall in love with them and laugh at the things they do and say, in which we may have experienced them in our life time.
In referring to character development, there isn't a solid base where we learn about the characters step by step. Instead, we are learning about them in a group while we are laughing and enjoying quality entertainment provided to us. Its how they socialise and the activities they do in which we learn so much about them.
In conclusion, a series in which is shouldn't be missed by the young and the old because series like these lifts your mood and gives you a smile on your face each episode of the way.
