Having a school website is no longer an option; it’s expected of every school to have a web presence. A website is more or less a window into your school. It showcases exactly what your school is about. However, it is also an advertisement for your school and a user’s first impressions may be the difference between a potential enrollment and someone not bothering.
This means the website should look as good as it can. If a school can afford to hire a professional designer, for me this would be the best possible option. With this option, you will get a completely personalised site. However, this can be very expensive.
Some companies offer a version of the above where they use a general template and personalise it to your school by changing the colour scheme, adding/taking away elements that you need, etc. These are a little cheaper than the first option and are generally quite affordable.
There are also templated websites that can be free such as Scoilnet Sites, Wix, Weebly and so on. These are a good option for those starting off because they look good enough to showcase your school and the templates are generally up to date and look well.
You can of course design your own site. This is where things can go terribly wrong or completely right. However, unless you have a good eye for design, the latter is usually the case. There was a trend a number of years ago for schools to use a service called WebX5 to create web sites and all of these websites look very dated these days.
Whatever option you choose, I would probably go with something based on WordPress. Scoilnet Sites is based on WordPress and is a good starting point. When you are ready to move from there, I would choose a company that uses WordPress as a backend.
Another consideration is to make sure you have a domain name. A website called http://schoolname.scoilnet.ie is not as attractive as a school http://www.schoolname.ie. It’s also good to use a .ie domain if you can. Although it is more expensive than .com or .org or .net sites, it shows that the school is Irish.