CLASS-MON, an add-on for Google Sheets helps teachers identify students' difficulties. The teacher introduces the list of activities that the students must carry out. CLASSMON automatically creates a form with all activities and the following response options: I didn't do the task. I performed the task with many doubts. I performed the task with some doubts. I did the task and I think I got it. When a student finishes an activity, he/she answers the form. The teacher can always see the students' difficulties. He can also detect the most complicated activities.