Using email to communicate with the teacher takes the child out of the equation. Generally people can access their email throughout the business day, so teachers can receive notifications about children being late, send notifications about after-school detention, report missing homework or failing grades, etc. For notifications to all parents, teachers request emails from parents at the beginning of the year and from time to time, send group emails to parents to notify them of upcoming tests, deadlines, field trips, events, etc.
Building a website on a free service such as Wordpress, Blogger, or Typepad allows the teacher to write a blog. Parents can subscribe to posts by the teacher and then leave comments on the posts as a means of communication. The teacher can post details about what the class is learning, unit studies, and academic schedules for the coming week. Teachers can also post links to online resources that parents can access in order to help their children with homework, or further understand the topic. However, a blog such as this will be a public forum. Many school websites also allow teachers to create their class page where they can post similar information for the benefit of parents.
Providing the teacher with a cell phone number allows instant access to the parent. Teachers can use this number not only to communicate concerns regarding a student's progress, but also during an emergency.
Many school districts have access to an online grading system that displays attendance, homework, test, report card and midterm grades. Parents can log on to access just their child's account, and the teacher can send notifications when there are updates.