The Literacy Promise conference I sat in on Brad Wilcox's presentation about inspiring students to write. One of the things that he mentioned was having high school students edit the writing of elementary school students. As Brad said during his presentation, "high school students don't care about comma placement in their own work, but they care about it when it is an elementary school student's work because they don't want to give bad directions." He went on to suggest having elementary school students put their writings in an envelope and addressing it to students in their district's high school.
Google Documents is designed for exactly what Brad Wilcox described in his presentation at The Literacy Promise conference. If your school district is using Google Apps for Education, sharing the documents is very easy to do. Have the elementary school students share their documents with a high school student, that student's teacher, and yourself. When the document is shared between all four of you, you and the other teacher can make sure that the suggestions made by the high school student are correct. Introduce all of the students to using the commenting feature in Google Docs to write comments and corrections in the margins of documents. By using the commenting feature, the actual changes to the document have to be carried out by the elementary school student.
If you want to learn how to use Google Documents, including the commenting feature, please read my free ebook Google Documents for Teachers.