In dealing with this topic, it helps to have an overview of the socialization, emotional, systemic, and institutional factors that contribute to teachers having sex with kids.
In the area of socialization, a lot of the factors that led to scrutiny and communication by and between parents and their children have drastically changed. Children are now encouraged to speak up when an adult attempts to engage with them in an inappropriate sexual fashion. Conversely, children are becoming sexualized at an earlier age.There is far more reporting, in far more detail, about incidents where teachers engage in inappropriate behavior. It is no longer the "who" that is talked about, the "how" and "why" is also investigated and reported widely. In conflict, more parents are dysfunctional due to drug and alcohol abuse and are not actively involved in their children's lives, leaving them vulnerable to inappropriate relationships with many adults in their lives.
In the area of emotional development, if the 30s are the new 20s, then the maturity of young teachers is closer to their students, and these young adults may be taking the easy way out with 16 and 17 year olds than with partners from their own age groups. Child molesters and predators are notorious for gravitating toward fields where they have access to and authority over children. But in this day and age, convicted molesters are permanently identified and prohibited from working as teachers of children.
In the systemic area, there have always been teachers who gave into their urges and had sex with children under their care. It is just that now, the reporting is improved, abusers have been identified and thrown out, and there is much more awareness in the community. This does not prevent or eliminate the problem, but the consequences and likelihood of being caught are higher than they have ever been.
Institutional: Parents are often distant and uninvolved in the school. They do not volunteer to work closely to the school and may not even be that involved in their own neighborhood, let alone the issues that are going on between their children and teachers. Schools, and class sizes, are huge. There is no longer "the little red schoolhouse" or the neighborhood private school, where the whole community kept track of everyone and everything that went on. This social disconnect from the sheer size of school operations provides opportunity for predation to go on undetected.
As a result, many factors, elements of opportunity, programs which capture and prevent, the emotional states of young adults and children, and the size and anonymity of schools and their communities contribute to incidents where teachers engage in sex with children.