Page-level permissions in Google Sites allows the creator of a site to share and give editing access to specific pages within a site rather than giving access to edit the entire site. To use page-level permissions open your Google Site editor then click "enable page-level permissions." With page-level permissions activated you can share and allow editing for each page individually.
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Applications for Education
By using page-level permissions in Google Sites you can create a classroom website then make each of your students responsible for maintaining their own pages. On those pages they could catalog examples of their best work. They could also use those pages to blog. Either way you will have access to work from all of your students in one place.