Preparing spreadsheets or Word documents is a significant hassle for the class rep. It takes ages for everybody to sign up, and once they do, details change and need to be corrected. Parents then have to find the right spreadsheet, somewhere in their email. More importantly, sending sensitive information as an email attachment is far from secure. Many email systems are relatively open to attack particularly when transmitting unencrypted files.
Once the email and attachment arrives on another parent's device it is far from secure. There is no way of knowing whether the attachment - containing your family's private details - has been distributed further; whether the device is protected; and who can access it. Your information stays on somebody else's device for months or years, with devices sometimes passed to others inside or outside the family. There is no requirement for the device owner to report any security breach and no way of retrieving or closing down access to your information should this occur. Spreadsheets can easily be printed out and carried around, with obvious security risks. In contrast, entering and managing your own data through a fully managed website using up-to-date industry security protocols, where site operators have the ability to control access, manage users, and detect attacks, offers far greater security. It also gives users much more choice over what information they wish to supply, or retract, at any particular point in time. If any parent is found not respecting another's privacy they will be removed from the site.