Having a reason to write and a real audience can make a huge difference in student motivation to write. Many schools are in the process of setting up filtered or monitored email accounts for student use. By having an email account, the student will have an opportunity to learn about Acceptable Use Policies, Neticate, and other online issues.
Net is one free, filtered email service for schools.
There are a variety of free email accounts available. Many people use yahoo or hotmail accounts for their personal mail. There are services to school's that offer more monitoring and control of student's access. Check with your school's technology specialist to find out if there are services the school has agreed to use. Check out recommended services by other educational groups.