How to tell Ember.js that Array has been updated

I have been reading the documentation for a while now and cannot figure it out. I have the following code:

App.User = DS.Model.extend({
   name: DS.attr("string"),
   points: DS.attr("float"),
   isPassing: Ember.computed.gt("points", 65),
   isEditingPoints: DS.attr("boolean", {defaultValue: false}),
   isEditingName: DS.attr("boolean", {defaultValue: false})
});

App.User.FIXTURES = [
   {
      id: 1,
      name: "Joe",
      points: 85
   },
   {
      id: 2,
      name: "Cindy",
      points: 90
   },
   {
      id: 3,
      name: "Ben",
      points: 62
   }
];

App.UserController = Ember.ObjectController.extend({
   actions: {
      editUserName: function() {
         this.set("isEditingName", true);
      },

      editUserPoints: function() {
         this.set("isEditingPoints", true);
      },

      acceptPointChanges: function() {
         this.set("isEditingPoints", false);

         if(Ember.isEmpty(this.get("model.points"))) {
            this.send("removeUser");
         }
      },

      acceptNameChanges: function() {
         this.set("isEditingName", false);

         if(Ember.isEmpty(this.get("model.name"))) {
            this.send("removeUser");
         }
      },

      removeUser: function() {
         var user = this.get("model");
         student.deleteRecord();
      }
   }
});

App.EditUserView = Ember.TextField.extend({
   didInsertElement: function() {
      this.$().focus();
   }
});

Ember.Handlebars.helper("edit-user", App.EditUserView);



App.ApplicationController = Ember.ArrayController.extend({
   actions: {
      createStudent: function() {
         var newName = this.get("newName");
         var newPoint = this.get("newPoint")
         var parsePoint = parseFloat(newPoint, 10);

         if(!newName.trim() || isNaN(parsePoint)) {
            return;
         }

         Count++;

         var student = this.store.createRecord("student", {
            id: Count,
            name: newName,
            points: parsePoint
         });

         this.set("newName", "");
         this.set("newPoint", "");
      }
   },

   AverageScore: function() {
      var UserInfoArray = this.sortBy("id");

      var sumOfPoints = 0;

      console.log("ran AverageScore");

      for(var i = 0; i < UserInfoArray.length; i++) {

         var UserData = UserInfoArray[i]._data;
         var UserAtt = UserInfoArray[i]._attributes;

         if(isNaN(studentAtt.points)) {
            sumOfPoints += studentData.points;
         } else {
            sumOfPoints += parseFloat(studentAtt.points,10);
         }
      }

      if(sumOfPoints == 0) {
         return "None";
      }
      return sumOfPoints/UserInfoArray.length;
   }.property("@each")

I am trying to get the average of each user's points but whenever I update the App.User it does not run the AverageScore function again. I would like it to run every time I update an item in the array of users. However it only updates every time I remove a user from the dataset. How can I make it update on each change?