Andes: An Intelligent Tutor Homework System

Demo presented at ITS 2008, Montreal.

Andes is an intelligent tutor homework system designed for use in a standard two-semester introductory physics course.  It has been used in the classroom at the US Naval Academy since 2000 and has been used sucessfully at other colleges and at the high-school level.  Several semester-long evaluations of Andes showed that students who did their homework on it learned significantly more than students who did the same homework problems on paper.  In this demo, you will solve a typical Andes problem while watching an example solution (in case your physics is a little rusty).  During this exploration, we will introduce you to some of the important features of Andes:  emphasis on good problem solving technique, immediate feedback, hinting strategies, model tracing strategy, and grading policies.

Example Andes screenshot

Figure 1:  The Andes screen has areas for the problem statement and student-drawn diagrams, defining quantities, and entering equations.  The lower left area is where the tutor gives hints.  Student entries turn green if it is correct or red if incorrect.  In this example, the equation has turned red and the student has subsequently asked for a number of hints. 

The Andes user interface is designed to behave like pencil and paper.  A typical physics problem and a partially completed solution are shown in Figure 1.  Students read the problem (upper left area), draw vectors and coordinate axes (also upper left area), define variables (upper right area) and enter equations (lower right area).  These are the actions that students should perform when solving the same problem with pencil and paper.

Unlike paper, however, variables are defined by filling out a dialogue box.  Vectors and other graphical objects are first drawn by clicking on the tool bar on the left edge of the window, drawing the object using the mouse, and filling out a dialogue box.  Dialogue boxes require students to precisely define the semantics of variables and vectors. 

Good problem solving technique

Andes encourages students to use the problem solving strategies that physics instructors value: student must define quantities, draw diagrams, use units, and write down intermediate steps in a solution.  It encourages students to work with algebraic (rather than numerical) expressions.  When solving a problem, students must identify implicitly which principle of physics they are using by writing down an equation that is isomorphic to the equation associated with that principle.

Immediate feedback

Unlike a piece of paper, as soon as an action is completed, Andes gives immediate feedback.  Entries are colored green if they are correct and red if they are incorrect.  In Figure 1, all the entries are green except for the equation, which is red.

Hinting strategies

Andes provides three different kinds of instructional assistance:

Thus, for errors that are likely to be careless mistakes, Andes gives unsolicited help, while for errors where some learning is possible, Andes gives help only when asked. 

What's Wrong Help and Next Step Help usually generate a hint sequence consisting of pointing hints, teaching hints, and bottom-out hints.  For example, in Figure 1, the student has forgotten to draw one of the vectors.  These are the What's Wrong hints that Andes gives:

  1. There is a force acting on the ball at T0 that you
    have not yet drawn.
  2. Notice that the ball is supported by a surface: wall2.
  3. When an object is supported by a surface, the 
    surface exerts a normal force on it.  The normal force
    is prpendicular to the surface.
  4. Because wall2 supports the ball, draw a normal 
    force on the ball due to wall2 at an angle of 40 
After each of the first three hints, Andes displays two buttons labeled "Explain more" and "OK."  If the student presses "Explain more," they get the next hint in the sequence. 

Model tracing strategy

The hints in Andes are generated by comparing the student actions to a model solution of the problem.  The model solution (or set of solutions) is supposed to represent the way an expert thinks about a problem.  Thus, for "Next Step Help," it matches the student entries to a model solution to determine how much of the model solution has been completed and provides hints associated with the first uncompleted step in the model solution. 


As the student solves a problem, Andes computes and displays a score.  The score is based on the number of correct entries with penalties for the number of incorrect (red) entries and the number of bottom-out hints received.  The penalty on the bottom-out hints encourages the student to use the help but discourages help abuse.  Andes puts little weight on the final answer, encouraging students to "show their work."