Starting a blog is easy. Sign up for a free classroom blog at a website such as:

www.edublogs.org

www.wordpress.com

www.blogger.com

There are tons of blog spots out there so pick one that fits your needs. Edublogs is specifically designed to be used in education so it's always a good start.

If you want students to have their own individual blogs kidblog.org is a great site. You create the password and username for students so that it is private and students don't have to have an email to join. You can create a class with all your students to easily monitor and make sure everything is kept safe.