inductor is twice as large as the voltage of the voltage
students to respond when they are ready, instead of all
source. This discomfort can be a good thing — it pro-
at once. The system also records the results of each
duces a teachable moment, when students are recep-
concept test for later analysis.
tive to ideas that challenge their view of the world. Student responses to the concept tests can be gathered
MUDDIEST POINT IN THE LECTURE
in different ways. Initially, we used flash cards, with
Another active learning technique that we have used
students presenting their answers simultaneously. A
with success is the “muddiest point in the lecture”
quick scan of the room is sufficient to determine
technique, credited to Harvard Professor C. Frederick
approximately the rate of correct and incorrect
Mosteller. In this approach, students are asked to take
responses. Flash cards are cheap, easy to use, and con-
two minutes at the end of each lecture to write the
fidential (since, if students are seated facing in the
most confusing (or muddiest) point of the lecture on
same direction, each sees only the backs of other flash
an index card, and hand it in to the instructor (Fig. 2).
cards). However, there are a number of drawbacks to
Some instructors also ask students to identify the most
flashcards that led us to begin using an electronic
important point of the lecture. These muddy cards, as
response system, the Personal Response System brand
we call them, serve two useful functions. First, they
infrared system. For example, with flash cards, it is
give students time to reflect on their learning.
difficult to capture student response for later analysis
Reflection is an important activity to reinforce learn-
by the instructors. In a typical classroom installation
ing, but is not practiced often in the high-pressure
of the PRS system, each student has a hand-held
atmosphere of an MIT education. Second, the muddy
infrared remote transmitter, much like a television
cards provide direct feedback to instructors on prob-
remote control. During a multiple choice concept
lems students are having in class.
test, each student indicates his or her answer by pressing a single digit on the remote keypad. An infrared receiver connected to a personal computer collects the student responses, and displays the result in histogram form to the instructor. The electronic system allows
Instructors can act on the information in muddy cards in several ways. They can use part of the next lecture hour to discuss common muddy points. Instructors in Unified often use the Web to post responses to questions on the muddy cards. Or, instructors can simply
Teaching by Questioning
33