ugradtas.txt

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              Using Undergraduates as Teaching Assistants
                  in Introductory Programming Courses:
                  An Update on the Stanford Experience

              Eric Roberts, John Lilly, and Bryan Rollins
                     Department of Computer Science
                          Stanford University


NOTE

This paper has been submitted to the Twenty-sixth SIGCSE Technical
Symposium on Computer Science Education.  Copyright is retained by the
authors prior to publication release.

ABSTRACT

The introductory computer science classes at Stanford University have a
combined annual enrollment of over 1000 students.  Teaching introductory
programming to a population of this size requires significant
instructional support to ensure that students receive the individual
attention most beginning programmers need.  This paper describes the
approach that has evolved at Stanford for the introductory computer
science courses, which is based on the extensive use of advanced
undergraduates to teach sections of the introductory course.  In our
experience, using undergraduates as part of the teaching staff has
created an effective learning environment for both the students in the
classes and the undergraduate section leaders themselves.

1.  INTRODUCTION

For more than a decade, the Computer Science Department at Stanford
University has used undergraduate students to supplement the
instructional staff in the introductory programming courses.  The
typical introductory course is assigned one lecturer, one graduate
teaching assistant, and a large number of undergraduate course
assistants, called "section leaders."  The lecturer is responsible for
presenting the class material and designing assignments and exams.  The
graduate TA helps the lecturer with course content and administration.
The section leaders conduct weekly small-group discussion sections,
grade assignments, and assist students working in the computer cluster.

In 1988, Stuart Reges, then the director of Stanford's computer science
education program, presented a paper at the SIGCSE conference describing
Stanford's initial experiences with the section-leading program
[Reges88].  In that paper, Reges discusses the following advantages of
the program:

   o  Undergraduate section leaders are less expensive than
      traditional graduate TAs.
   o  Undergraduate section leaders, having more recently been in
      the same position, are better able to establish a rapport with
      introductory students.
   o  Undergraduates are more familiar with the Stanford computing
      facilities and curriculum than most graduate students.

While these arguments continue to apply, our six additional years of
experience have demonstrated several other positive features of the
section-leading program:

   o  Having the opportunity to teach new students is of enormous
      benefit to the section leader as well.  In the process of
      explaining concepts to each new class, the section leader's
      own understanding of those concepts grows dramatically.
      Similarly, encouraging students to use good programming style
      usually improves the section leader's programming style as
      well.  Thus, the section-leading program becomes an integral
      part of the section leader's own undergraduate education.

   o  The section-leading program has a salutary effect on the
      entire undergraduate department, even though only about 25
      percent of CS majors participate in the program (which also
      includes students from many other fields).  Their shared
      experience creates a strong connection among the section
      leaders, which gives rise to many activities that benefit the
      community as a whole.

   o  The section leaders, occupying as they do a position of
      significant trust and responsibility, become role models for
      younger students.  That modeling is all the more effective
      because the section-leader's role is one that an introductory
      student might assume, not in ten or twenty years, but in one
      or two.  The fact that the path to becoming a section leader
      is well-marked gives many undergraduates a powerful incentive
      to succeed.

   o  The section-leading program serves as a training ground for
      future lecturers.  Seven of the 13 people hired as
      departmental lecturers over the past decade were formerly
      Stanford undergraduates involved in the section-leading
      program.  By participating in the program, section leaders
      develop excellent teaching skills that serve them well in more
      advanced teaching positions.

In short, we are more convinced than ever that using undergraduates as
section leaders has significant pedagogical advantages, both for the
introductory classes and for the program as a whole.  Moreover, other
schools such as Brown University and the University of Virginia are
beginning to rely more on undergraduates for teaching assistance.  Thus,
we thought it was appropriate to update the 1988 Reges paper and offer a
more detailed analysis of the Stanford approach.

2.  INTRODUCTORY CS COURSES AT STANFORD

In order to appreciate the structure of the section-leading program and
how it fits into the curriculum, it is necessary to know something about
the Stanford computer science program as a whole and, in particular,
about the scale at which it is conducted.  At present, we estimate that
75 percent of Stanford undergraduates take at least one introductory
programming course offered by the Computer Science Department.  To
appeal to students with a wide range of interests and prior experience,
the department offers several different introductory courses:

  CS105   Introduction to Computing

  CS106A  Programming Methodology
  CS106B  Programming Abstractions

  CS106X  Accelerated 106A + 106B

CS105 is intended for nontechnical students, most of whom are seeking to
satisfy Stanford's undergraduate requirement in technology and applied
science.  The CS106 courses offer a more traditional introduction to
programming that follows reasonably closely the CS1/CS2 curriculum
outlined in Curriculum 78 [Austing79].  The CS106A/CS106B sequence
covers this material in two quarters and is designed for students with
little or no programming experience.  CS106X covers the same material in
a single quarter and is designed for students with more extensive
programming backgrounds.[1]

As at most universities, enrollments in Stanford's introductory
programming courses skyrocketed in the late 1970s and early 1980s,
increasing by a factor of three in the decade between 1975 and 1985.
Since 1985, enrollments in the introductory courses have remained
relatively constant, as illustrated by the following table showing the
total annual enrollment in all sections of CS106:

                                  Total CS106
                          Year    Enrollment
                          85-86      1000
                          86-87      1119
                          87-88       959
                          88-89      1006
                          89-90       981
                          90-91       922
                          91-92       845
                          92-93      1016
                          93-94      1112

From 1986 to 1991, enrollments in CS106 registered a downward trend.
This decline, however, was reversed when we changed the programming
language from Pascal to C at the end of the 1991-92 year [Roberts93].

It is also interesting to note that most undergraduates --  even those
who are majoring or intend to major in a nontechnical field -- tend to
take one of the CS106 courses rather than the nontechnically oriented
CS105.  Typically, only about 300 students take CS105 each year.  By
contrast, the combined enrollment in CS106A and CS106X (covering the two
paths through the CS106 sequence) is approximately three times that
size.

The CS106 series is popular because

   o  The courses are regarded as highly practical, particularly now
      that they use ANSI C.
   o  CS106 fulfills an Engineering School requirement, while CS105
      does not.
   o  CS106 has an excellent reputation in the undergraduate
      community for high-quality teaching.

Course evaluation statistics support the good reputation of CS106.  The
following table summarizes the student ratings for all CS106 courses in
1993-94 in comparison to all courses in the Engineering School:

                                CS106    All engineering
                               courses       courses
               1 (excellent)     63%           44%
               2 (very good)     31%           34%
               3 (good)           5%           14%
               4 (fair)           1%            6%
               5 (poor)           0%            2%

As these statistics indicate, 94 percent of the respondents rate CS106A
as very good or excellent.  In 1994, one of the undergraduate newspapers
named CS106A as one of the five best courses at Stanford.

The reputation of the CS106 courses is further enhanced by the section-
leading program, which supports all the CS106 courses but not CS105,
whose design is more conventional in that all teaching assistance is
supplied by graduate TAs.[2]  The section leaders act as ambassadors for
the CS106 program in the undergraduate community and encourage other
students to take those courses.

3.  RESPONDING TO LARGE ENROLLMENTS

The combined enrollment for all sections of CS106 in 1993-94 was 1112.
Teaching introductory programming at this scale places considerable
demand on the resources of the Computer Science Department.  Although
computer science professors represent only two percent of the total
university faculty, computer science courses account for five percent of
the total student units, with much of the additional demand for
instruction coming from the introductory courses.  This imbalance
between faculty size and enrollments means that the Computer Science
Department carries two and a half times the average instructional load
per faculty member -- a level that cannot be sustained without
jeopardizing Stanford's preeminent position as a computer science
research institution.

To reduce the teaching load to a level more consistent with that in the
rest of the Engineering School, Stanford appoints lecturers to
supplement the regular faculty.  Lecturers are chosen entirely on the
basis of demonstrated teaching ability and are not expected to conduct
research.  The positions are renewable but not eligible for tenure.
Currently, the department employs five lecturers, two of whom work
part-time, so the total lecturer strength is the equivalent of 4.25
full-time positions.  In addition, the Associate Chair for Education, a
faculty-rank position within the department currently held by Eric
Roberts, oversees the entire teaching program.

The lecturers, as talented as they are, would not be able to do such a
good job with these large courses without assistance.  Teaching
introductory programming effectively requires that students be able to
interact with someone who understands the material, particularly when
questions arise in the context of a programming laboratory or a homework
assignment.  Introductory programming courses tend to require a large
number of student contact hours, far more than would be possible if the
lecturer had to cover this aspect of the class as well.  At Stanford,
most of the teaching support required for the introductory courses is
supplied by the section-leading program, which is described in the next
section.

4.  SECTION LEADERS

In a typical quarter, the Computer Science Department hires
approximately 50 section leaders to staff the CS106 courses.  At the
beginning of each quarter, every section leader is assigned to a section
consisting of approximately ten students.  Throughout the quarter, those
students "belong" to that section leader, in that the section leader is
responsible for going over material with them in a weekly recitation
section, grading their programs, and being their link to the rest of the
class.  For instance, if students feel lectures are covering the course
material too quickly or that particular topics have been a little
confusing, the section leader can spend extra time on those topics
during section that week and make the lecturer aware of the section's
concerns.  This feedback mechanism is extremely important for large
lecture courses in which it is difficult for the lecturer to get an
accurate reading of the class as a whole.  This structure provides all
students with a small-group environment in which they are not merely one
student in a sea of 300 others.

For two hours a week, each section leader holds what we call "helper
hours" in the campus computer cluster, where they are available to help
any student who is working on a CS106 assignment.  These hours are
distributed among section leaders to cover approximately 70 hours per
week, with additional coverage during times of unusually heavy use.  We
believe that providing this type of readily available assistance is
extremely important for computer science in particular.  Students often
discover that they are having conceptual problems only when they reach
an impasse at the computer.  Having a staff member on call to explain
concepts, answer questions, and help the student discover the problem
not only makes an enormous difference in the level of student
understanding but also reduces the level of frustration associated with
the class.  In essence, the existence of a large section-leader
community makes it possible for Stanford students to enjoy the benefits
of closed laboratories on a round-the-clock basis.

The section leaders represent a diverse cross-section of the Stanford
undergraduate population.  In educational status, they range from
sophomores to students spending an additional year to obtain both an
undergraduate and a master's degree.  Although many of the section
leaders are computer science majors, a significant number come from
other fields, including biology, psychology, economics, political