Parental Involvement in Schools

As future educators, we have decided to explore the role of parents in their child's education. The involvement of parents in their child's education is a very tempermental one, since they, the parent, know exactly what their child needs. We have researched the multiple ideas and ways that parents can positively help both student and teacher in the classroom, as well as a couple of ways to let them know when they're not needed within the classroom.

How does involvement of parents affect the classroom atmosphere? What are the key aspects to a successful parent/teacher relationship? Why are some teachers reluctant about encouraging parental involvement? Links to sources