When you install Scientific Linux, it will keep you on the same point release that you installed. For example, if you install it from a 6.0 DVD, you’ll stay on 6.0 and get security releases for that point release only.
Getting it to behave like Red Hat Enterprise Linux and CentOS is a painless process. Just install the sl6x repository with
yum install yum-conf-sl6x
Check to ensure that you’re getting updates from the new repository:
# yum repolist repo id repo name status sl Scientific Linux 6.1 - x86_64 6,251 sl-security Scientific Linux 6.1 - x86_64 - security updates 548 sl6x Scientific Linux 6x - x86_64 6,251 sl6x-security Scientific Linux 6x - x86_64 - security updates 548 repolist: 13,598