Blogs are naturally "publish at will" platforms. While blogs certainly CAN be configured to have new posts "moderated" by someone serving in the role of a gatekeeper, by default most blogs allow users to publish INSTANTLY. If you're interested in setting up a blog for moderated posting by students, I'd recommend using Class Blogmeister for this purpose. Wordpress blogs can be configured for contributor posts to be moderated as well, but this requires a bit of configuration. (This is the setup we're using here on ISTEconnects, btw.) On the Wordpress dashboard, under SETTINGS - GENERAL SETTINGS, we've checked the MEMBERSHIP box ANYONE CAN REGISTER and set the "New User Default Role" to be CONTRIBUTOR. With these configuration settings, new posts must be reviewed by a user designated as an "editor" or "administrator" before they become "live" on the site. For more on this, see the Wordpress.org CODEX article "Roles and Capabilities." To setup a free classroom or personal Wordpress blog you don't have to host yourself, I recommend using EduBlogs or Wordpress.com. Blogs setup with Blogger can similarly be setup as "team" blogs with moderated contributions from members which can include students and/or teachers. See the Blogger help article "How do I create a team blog?" for more details. My post from July 2008, "How can our school set up a team blog for teachers?" also gives more information about this for Wordpress users.
"Class Blogmeister is one of several blogging engines that \nhave been developed specifically for classroom use. You are welcome to explore \nthe writings of teachers and students alike."