Many schools have blocked Blogger because of the "Next blog" button at the top of the page. Clicking this button causes a random blog to appear on your screen-- and who knows what might show up!
There is a work around for this problem that involves a little bit of template code hacking. I am quoting this solution I found posted in the comments of this post on Will Richardson's blog:
"The move to New Blogger simply required a different bit of code…add the following lines anywhere in the template [enclosed by tags] and the blogger banner will disappear.
This removes the whole navbar at the top of the blog, which solves our NEXT BLOG dilema…"