Htaccess Problem - sub.domain.com redirect to www.sub.domain.com

[curb]

I'm currently using this in my htaccess so when a user inputs "school.com", it will redirect them to "http://www.school.com/".

RewriteEngine on
RewriteCond %{HTTP_HOST} ^school.com
RewriteRule ^(.*)$ http://www.school.com/$1 [R=301]

I now have a subdomain and I want the same thing to happen when a user inputs "class.school.com" to redirect to "http://www.class.school.com/"

RewriteEngine on
RewriteCond %{HTTP_HOST} ^{class.school.com}
RewriteRule ^(.*)$ http://www.class.school.com/$1 [R=301]

The problem is it won't redirect it and it'll land on "http://class.school.com/" with a 'Page Not Found'. How would this be possible?

[Hendricus]

Is http://www.class.school.com an actual subdomain?

Maybe this will help ya:
http://www.ilovejackdaniels.com/mod_rewrite_cheat_sheet.png

[curb]

Yes, the http://www.class.school.com is an actual subdomain

[Horizon88]

If I remember correctly, .htaccess rules get processed top-down, so try setting it like this:

RewriteEngine on
RewriteRule ^(.*)$ http://www.class.school.com/$1 [R=301]
RewriteCond %{HTTP_HOST} ^class.school.com