2. Limitations of the study
It should be noted that the present study was carried out in
the context of a normal course in physics, thus offering
ecological validity to the aforementioned findings. On the
other hand, the study had some limitations related to the time-
framework that was followed for the data collection. First, the
data for the control group were derived from a former study of
the authors that was conducted about two years before the
collection of the data that concerned the experimental groups
of the present study and, second, the experimental groups were
not all run concurrently. Yet, the students of the control group
were not found to differ, either in the nature and type of their
conceptions or statistically in their pre-test performance from
that of the students in the experimental groups (both studies
used the same pre-tests). Additionally, all students followed
the same curriculum, Physics by Inquiry, and all students had
the same age and educational background. Another limitation
of this study is that it involved only one data source
(conceptual tests). We could have had a better insight in terms
of student learning that took place during our intervention, if
we had used more data sources, particularly data sources
focusing on the process rather than just the end results. For
instance, in the case of VME, we could have taken on-line
measures of learning.
However, despite these limitations, the findings of the
present study still provide some valuable information. In
particular, findings like the ones of this study challenge the
already established norms concerning experimentation in the
physics classroom, as we experienced it through PME, in
a way that calls for a redefinition and restructuring of exper-
imentation to include VME. However, this call for reform
creates the need for understanding how PME and VME could
be integrated in teaching and learning activity sequences for
physics. Therefore, it is essential to extend the empirical base
through similar research in order to ground the perspectives
advocated in this study.