Google Sites – How to Give Editing Rights Without Google Account

@gerzan, you've asked a great question. This answer may be coming too late for you, but perhaps someone else can benefit from it.

Basically, what you're asking for can be established with Google Groups. If you're not familiar with the system, there are two key permissions we can set: "view topics" and "post". Both of these can be set from the creation URL: https://groups.google.com/a/schoolname.com/forum/#!creategroup (note: replace schoolname.com with your actual domain!)

1. Create a Google Group that contains all teacher addresses - let's call it teachers@schoolname.com. Set view and post permissions to "All members of the group" so teachers can easily converse (although we're primarily creating the group to ease access permissions, as you'll see later). Also limit "Join the group" to "Only invited users".
2. Create the class-specific groups you want, for example history101@schoolname.com. Set view and post permissions to "All members of the group" again. Limit "Join the group" to "Only invited users".
3. Go to the following URL to directly add members: https://groups.google.com/a/schoolname.com/forum/#!managemembers/history101/members/active (replacing the bolded values with your domain name and group name, respectively). Here, enter teachers@schoolname.com and set "Email subscription options" to "No email" so teachers don't get fed up with emails for classes they aren't teaching.
   4. After you add the teachers, add the other student accounts for this class. Then, anyone in the 'teachers' group will be able to send and any student in the class can send. (Bonus tip: you may want to add the teacher for this class and make sure they will receive "all email" from the group.

This is just one way to set up this model, let me know if you're interested in any others. Also, to manage group populations between semesters, I'd recommend looking at a tool like GAM where you can use CSVs and Powershell to quickly add/remove users from Google Groups.

I installed Vidar’s script and works very well for files, but wouldn't reset permissions on folders. So, I changed a little bit the code to make the folders also inherite the permissions from their upper folder.

Two important disclaimers:

1. I don't know if the original intention was to leave folders unchanged. Or even if it worked well for everybody but me, and this solutions was unnecesary. It worked for me.
2. This is the first script I do, so it is very likely that it is not very efficient and may content some errors. Please feel free to correct it and improve it.

I only changed the doResetPermissions function, but I paste all the code for simplicity reasons.

var selectedFolder;
var dialog;

function doGet() {
  var app = UiApp.createApplication();
  var heading = app.createHTML("<h1>Folders for</h1>");
  app.add(heading);
  var allFoldersIterator = DriveApp.getFolders();
  var text = app.createTextArea().setName("text").setId("output");
  app.add(text);
  var tree = app.createTree();
  var rootFolder = DriveApp.getRootFolder();
  var treeRoot = app.createTreeItem(rootFolder.getName()).setId(rootFolder.getId());
  var handler = app.createServerHandler("folderSelected");
  tree.addItem(treeRoot);
  tree.addSelectionHandler(handler);
  treeRoot.setState(true);
  createBranch(rootFolder, treeRoot, app);
  app.add(tree);
  var selectedFolderIdBox = app.createTextBox().setName("selectedFolderIdBox").setId("selectedFolderIdBox");
  app.add(selectedFolderIdBox);
  return app;
}

function createBranch(folder, branch, app) {
  var children = folder.getFolders();
  while (children.hasNext()) {
    child = children.next();
    Logger.log("Folder id: " + child.getId());
    var subBranch = app.createTreeItem(child.getName()).setId(child.getId());
    branch.addItem(subBranch);
    createBranch(child, subBranch, app);
  }
}

function folderSelected(eventInfo) {
  var app = UiApp.getActiveApplication();
  var parameter = eventInfo.parameter;
  Logger.log("Selected " + eventInfo.parameter.selected);
  selectedFolder = DriveApp.getFolderById(eventInfo.parameter.selected);
  var selectedFolderIdBox = app.getElementById("selectedFolderIdBox");
  selectedFolderIdBox.setValue(eventInfo.parameter.selected);
  var okHandler = app.createServerHandler("okResetPermissions");
  okHandler.addCallbackElement(selectedFolderIdBox);
  dialog = app.createDialogBox(true, true);
  var panel = app.createFlowPanel();
  dialog.add(panel);
  dialog.setId("confirmationDialog");
  dialog.setPopupPosition(100, 100).setSize(500, 500);
  panel.add(app.createLabel("Do you want to reset permissions for all files found in folder " + selectedFolder.getName() + " and its subfolders?\n (Click outside of the dialog box to cancel)"));
  panel.add(app.createButton("Do it!", okHandler));
  dialog.show();
  return app;
}

function okResetPermissions(eventInfo) {
  var selectedFolderId = eventInfo.parameter.selectedFolderIdBox;
  var selectedFolder = DriveApp.getFolderById(selectedFolderId);
  Logger.log("Resetting permissions on " + selectedFolder.getName());
  var app = UiApp.getActiveApplication();
  app.getElementById("confirmationDialog").hide();
  Logger.log("Confirmation dialog hidden");
  var progressIndicator = app.createDialogBox(false, true);
  progressIndicator.setId("progressIndicator");
  progressIndicator.setPopupPosition(100, 100).setSize(500, 500);
  var label = app.createLabel("Working ...");
  progressIndicator.add(label);
  progressIndicator.show();
  doResetPermissions(selectedFolder, function() {
    var app = UiApp.getActiveApplication();
    var progressIndicator = app.getElementById("progressIndicator");
    progressIndicator.hide();
    return app;
  });
  return app;
}

function doResetPermissions(selectedFolder, callback) {
  Logger.log("Resetting permissions on folder " + selectedFolder.getName());

  var sharingAccess = selectedFolder.getSharingAccess();
  var sharingPermission = selectedFolder.getSharingPermission();

  var viewersfolder = selectedFolder.getViewers();
  Logger.log("Number of Viewers in folder: " + selectedFolder.getName() + " = " + viewersfolder.length);
  for (var i = 0; i < viewersfolder.length; i++) {
    Logger.log("      Removing viewer " + viewersfolder[i].getEmail());
    selectedFolder.removeViewer(viewersfolder[i]);
  }

  var editorsfolder = selectedFolder.getEditors();

  Logger.log("Number of Editors in folder: " + selectedFolder.getName() + " = " + editorsfolder.length);

  for (var i = 0; i < editorsfolder.length; i++) {
    Logger.log("      Removing editor " + editorsfolder[i].getEmail());
    selectedFolder.removeEditor(editorsfolder[i]);
  }

  var files = selectedFolder.getFiles();
  while (files.hasNext()) {
    var file = files.next();
    Logger.log("   Resetting permissions on file " + file.getName());
    file.setSharing(sharingAccess, sharingPermission);

    var viewers = file.getViewers();
    Logger.log("Number of Viewers in file: " + file.getName() + " = " + viewers.length);
    for (var i = 0; i < viewers.length; i++) {
      Logger.log("      Removing viewer " + viewers[i].getEmail());
      file.removeViewer(viewers[i]);
    }

    var editors = file.getEditors();

    Logger.log("Number of editors in file: " + file.getName() + " = " + editors.length);

    for (var i = 0; i < editors.length; i++) {
      Logger.log("      Removing editor " + editors[i].getEmail());
      file.removeEditor(editors[i]);
    }
  }

  var children = selectedFolder.getFolders();
  while (children.hasNext()) {
    var child = children.next();
    doResetPermissions(child);
  }

  if (callback) {
    callback();
  }
}