When you sense that a child's family environment is not providing the needed regulation and security, the first she does well, and the areas where she is having some challenges.
Inquire about things the parents may have noticed at home. Throughout the conversation, quietly observe how organized and regulated the parent seems to be. Usually, if there is a severe problem with alcohol or drug abuse, the teacher may notice that the parent is not able to give a very good picture of how the child is doing at home.
Seek Additional Help
If you do sense that a serious situation exists, try to arrange further meetings. It would be very helpful to invite an appropriate member of the school's special services team to join you. This typically is the school psychologist or social worker. Let the parents know beforehand that you're hoping to have another expert at the meeting to contribute advice. The expert will try to win the parent's trust in order to be instrumental in getting continuing help for the family. In a case like this, the most important goal is to stabilize the child's home environment.
If it appears to be an acute situation, where a child is not being adequately fed, not protected from harm, and in fact, you sense possible danger to the child, the school needs to act quickly. This can involve alerting Child Protective Services or its equivalent in your community. But even if the situation is not so dire, provide ongoing support by holding frequent meetings with the parents and the appropriate professionals.
Create a Nurturing Atmosphere
Since there is very likely a lot of unpredictability and lack of regulation at home, due to what the parents are struggling with, try to provide as much security as possible in the classroom. Starting with the basics, make sure that the child is well fed when she comes to school. Try to establish a special relationship with her so that she has the comfort of a consistently nurturing adult in her life.
If possible, avoid moving the child from class to class or teacher to teacher. If she is changing preschool teachers each year, arrange to have someone in school who can remain in her life constantly. It might be the social worker or school psychologist or a volunteer who will continue to be in a mentoring relationship, since the child is going to need this extra security.
Foster a nurturing relationship between this little girl and the other children too. Every positive relationship that she has will help her to feel more secure and better about herself. If she is impulsive with other kids or gets hurt feelings very easily, help to mediate and negotiate.