I looked into whether many schools are blocking Yahoo Answers. I haven’t seen any evidence of that so far, but apparently Yahoo doesn’t allow children (under 13) to use the service:
Children under the age of 13 are not permitted to ask or answer questions on Yahoo! Answers nor establish communication with other Yahoo! Answers users.
You never would know since kids are asking for homework help there constantly. It looks like pretty much all Yahoo services (email, messenger, flickr, games) are restricted to those 13 or older, except for Yahooligans.
I know that it is obvious to many of those familiar with the web that most interactive sites (like forums) do not allow children under 13. But it is something to consider given the number of edubloggers advocating the educational potential of services like blogger, twitter, second life, multiplayer videogames, etc. Other sites and software applications with similar restrictions include:
You affirm that you are either more than 18 years of age, or an emancipated minor, or possess legal parental or guardian consent, and are fully able and competent to enter into the terms, conditions, obligations, affirmations, representations, and warranties set forth in these Terms of Service, and to abide by and comply with these Terms of Service. In any case, you affirm that you are over the age of 13, as the YouTube Website is not intended for children under 13. If you are under 13 years of age, then please do not use the YouTube Website there are lots of other great web sites for you. Talk to your parents about what sites are appropriate for you.
Photobucket, which is basically like flickr & youtube:
Users of the Services must be at least 13 years of age. Children under the age of 13 are not permitted to use the Service and no information of children under the age of 13 will be knowingly collected by Photobucket.
Blogger (and bloglines, livejournal):
You must be at least thirteen (13) years of age to use the Service. Google reserves the right to refuse service to anyone at any time without notice for any reason.
MySpace (you have to be 14):
By using the MySpace Services, you represent and warrant that (a) all registration information you submit is truthful and accurate; (b) you will maintain the accuracy of such information; (c) you are 14 years of age or older; and (d) your use of the MySpace Services does not violate any applicable law or regulation. Your profile may be deleted and your Membership may be terminated without warning, if we believe that you are under 14 years of age.
All EA Games & Sites (including pogo.com, simcity):
In order for children 12 years old and under in such jurisdictions to participate in online activities that require registration, we require prior written permission or other verifiable consent from a parent or guardian. In other jurisdictions, prior written permission or other verifiable consent may be required from a parent or guardian for children under 14 or 18 years of age.
Take 2 Interactive games & sites (like Civilization III) just half warns about it:
Take Two Interactive does not knowingly collect personal information from children 12 years old or under. We encourage parents to instruct their children to never give out their real names, addresses or phone numbers, without permission, when using the Internet.
Also Second Life, Gmail, Google Groups, iTunes, Twitter, and many others restrict those under 13. Most all web forums and other participatory sites have a standard legal disclaimer that you must 13 years of age or older. Google (search engine) and Wikipedia do not appear to have such a restriction. This is another reason, too, to have a bit of preference for open source alternatives (like croquet and project darkstar vs. second life), since we can customize them for use with younger students, such as edublogs has done (built off of wordpress).