app.js

    var requests = nestedStore.find(requestsQuery);
    
    console.log("\n");
    console.log('BEGIN');
    
    var responseSets = nestedEvaluation.get('response_sets');
    
    console.log(' responseSets BEFORE forEach:', responseSets.toArray());
    
    requests.forEach(function(request) {
      var student = nestedStore.find(Core360.Student, request.get('student_id'));
      var course = nestedStore.find(Core360.Course, request.get('course_id'));
      
      var set = nestedStore.createRecord(Core360.EvaluationResponseSet, {
        evaluation: nestedEvaluation.get('id'),
        student: request.get('student_id'),
        course: request.get('course_id'),
        responses: []
      });
      
      console.log(' set DURING forEach:', set);
      responseSets.pushObject(set);
    });
    
    console.log(' responseSets.length AFTER forEach:', responseSets.get('length'));
    console.log(' responseSets AFTER forEach:', responseSets.toArray());
    console.log('END');

model.js

Core360.Evaluation = SC.Record.extend(
/** @scope Core360.Evaluation.prototype */ {
  response_sets: SC.Record.toMany('Core360.EvaluationResponseSet', { isMaster: NO })
});

output.js

BEGIN
 responseSets BEFORE forEach: []
 set DURING forEach: Core360.EvaluationResponseSet({evaluation: 78 , student: Q1004 , course: null , responses: }) READY_NEW { __sc_super__=[unsupported: no toString() function in type object], storeKey=534, more...}
 responseSets.length AFTER forEach: 1
 responseSets AFTER forEach: [undefined]
END