I suspect there are three reasons for this.
1) The parents establish a good rapport with the teacher early on and may even have the kid bring knick knack gifts to the teacher from time to time. Teachers work more with kids whose parents are engaged.
2) The "cuteness" factor. If a teacher feels a child looks "adorable" she or he is not likely to be as hard on him or her as another child they consider unattractive. This actually has been shown to be true in the work world as well. Hot, thin, "beautiful people" get better treatment and more breaks than their less attractive counterparts.
3) Some kids learn early on how to "charm" adults by always telling them what they want to hear or anticipating what they want. My best friend in high school was a guy named Rodney. Every time he saw my mother he would hug her and call her "mom". My mother would often say to me, "You should be more like Rodney". Little did she know he often threw parties when his parents were out of town, skipped school and had sex in his parent's bed...etc LOL!