In reality, it turns into a mess unless the website is organized. And teachers are not necessarily good website architects[*].
The school may have a website. Good. In a content management system like Drupal. Okay. With pages for every class, a news system, etc. Not so bad.
But then some teachers may use a separate Moodle.
And some other teachers may use a separate Google Apps or Google Sites site,.
So, for class #1 you have to go to the Drupal site. For class #2 you have to go to the Moodle. For class #3, the homework is posted on the Google Sites site, but there's some background info on the Moodle. And, oh yes, still other stuff on the Drupal.
AAARGH!!!! I can't remember which webtool - Drupal, Moodle, Google Sites - to use for any particular class. Yes, I may be a Luddite parent - but I am a reasonably web.savvy Luddite parent.
And it's not just me, the Luddite parent, who finds this confusing. The students do too. Not just my kid: I have had a teacher complain to me that this teacher keeps telling the class to use the Google Sites site for the class, but the students never seem to understand. Could it be because this teacher is their only teacher using Google Sites instead of Drupal or Moodle, and the kids naturally look to one place? Perhaps if this teacher created a class page in standard place on the Drupal or Moodle page, and linked to the Google Sites site for his class? It might also help the Luddite parents.
Note that above at the [*] I decided to say "website architect" or "website organizer" rather than "website designer". Website designers, at least the not so good ones, often concentrate on visual flashy effects. School websites have plenty of that. What they seem to lack is organization, or architecture.
Note: it's not just a question of installing a new content management system. They already have more than enough. Note that I am not saying "too many" - I am saying "more than enough". I am not against using different CMSes. But, if you do, you need to link them together, so you can get from one to the other.
Here is a dream, a suggestion a modest proposal for school websites:
(0) Have a front end, in whatever CMS you want. Drupal, say.
(1) Allow the teachers to create sites in whatever other CMSes they insist on using. Moodle. Google Sites. Whatever.
(2) But insist that there be a classroom page created on the front end site (Drupal, in this example). If nothing else, it should point to where on the other CMSes the real classroom contents.
Note that I don't mean just with text saying "some teachers use the Moodle or other tools". Which basically means that you have to figure out how to get there on your own. No, I mean a real, clickable, link to that other site. If you can't create a link into that other site, well... (IMHO that's the only reason to forbid using a different tool.)