They'll block malicious websites and other types of inappropriate sites, depending on the server you choose. (howtogeek.com)
Yes, a school should teach students what is acceptable, but — students being students — some will access inappropriate sites if no filter is used. (educationworld.com)
By default, nearly every website is blocked, so you won't have to worry about any faulty filters letting inappropriate sites through. (laptopmag.com)