mathematics of the statement being justified, none of the
responses suggested possible limitations of examples or
discussed how certain kinds of examples are preferable to
others from the standpoint of making a convincing argu-
ment. It remains unclear from the responses whether
students’ examples-based reasoning is what Balacheff
(1988) refers to as “naïve empiricism,” or whether stu-
dents at this level have begun to think more strategically
about example choice. Perhaps the lack of discussion
about the type or quantity of examples provided
was because of the EB argument in the item; the EB
argument in the Consecutive Numbers Task featured
three examples, one consisting of consecutive numbers
between 0 and 10, another consisting of consecutive
numbers between 10 and 20, and then a final example
consisting of consecutive numbers greater than 1,000. If
the item had contained multiple EB arguments, where the
sample arguments varied which examples were presented
as well whether examples were supported with written
explanations, students’ justifications for why the EB
argument was more convincing might have revealed more
about students’ attention to what examples communicate
mathematically.
While students repeatedly mentioned strengths in the
EB argument’s communicative function, as opposed to its
value in verifying the truth of a statement or explaining
why the statement is true, this finding is not surprising
given how omnipresent examples are in the teaching of
mathematics. Rowland (2008), citing Bills et al. (2006),
discusses how examples have been used to teach math-
ematics since antiquity. We should expect students to rec-
ognize that generating arguments and doing proof in
school mathematics have a didactical purpose rather than
the purpose of generating new knowledge or verifying the
truth of a statement for the discipline of mathematics.
However, as Levenson (2010) claims, teachers should
make explicit attempts to use more “mathematically
based” rather than examples-based explanations in their
instruction if students are to have opportunities to
develop the notion of proof in school mathematics
classrooms.
Herein lies a dilemma for teaching proof1: how can
teachers necessitate the use of valid, deductive forms of
reasoning without turning the act of proving a mathemati-
cal statement into an exercise so that students can prac-
tice doing proofs? Is it possible for students to understand
the various functions of proof, as well as the limitations
and acceptable uses of examples, if they are asked to
learn how to engage in proving by generating proofs for
statements already known to be true? Unlike other math-
School Science and Mathematics
ematical practices, the challenge of teaching proof is the
inevitable inauthenticity of proving situations within
school mathematics classrooms. Our study suggests two
implications for instruction. First, students should be
involved in discussions about what examples can show us
in mathematics. Using the “convince yourself, convince a
friend, convince a skeptic” (Mason, Burton, & Stacey,
1982) phrase can be helpful when students are being
asked to provide a justification. Second, it is important to
foreground for students why they are engaging in justi-
fying and proving. Because justification can be used to
not only explain why an idea is true but also establish that
a statement is true so it can be used for further math-
ematical investigations, students’ awareness of these dif-
ferent purposes can help them to consider whether
examples are sufficient for achieving those purposes. By
reinforcing these norms for generating and evaluating
justifications in a classroom, students learn to consider
and question the ways that teachers explain mathematical
ideas and press for more convincing explanations.
Conclusion
Although existing work documents the prevalence of
empirical reasoning in the proofs that students across all
grade levels generate, the findings of this study open the
possibility that students are not depending solely upon
examples to do the work of justifying and proving but are
instead employing examples as rhetorical devices to dem-
onstrate the mathematics of the statement being proven.
This echoes work of Chazan (1993) who found that high
school geometry students also found a valid proof to be
one where the argument provided contained both an expla-
nation and supporting examples.
The findings of this project also suggest that the emer-
gence of students’ preferences for arguments that both
show with examples and explain why may not only signal
their adoption of norms of school mathematics, such as
how a teacher shows examples while explaining how or
why a mathematical concept or procedures is true, but may
also signal growth in their abilities to generate mathemati-
cal arguments that treat the general case. While the inter-
view items were not specifically designed to distinguish
between the proof schemes students used to ascertain and
persuade, the results of our work suggest that students,
even at the middle-school level, distinguish between what
is personally and what is publicly convincing when engag-
ing in evaluating arguments.
This study is limited by its small sample of interview
responses and the choice to examine interview responses
to arguments from only one topic of mathematics.