Differences in the Distribution of High School Achievement: The Role
of Class Size and Time-in-term
by Miles Corak and Darren Lauzon
Family and Labour Studies Division
Analytical Studies Branch research paper series, No. 270
Context
Variation in school outcomes across jurisdictions raises important
questions about equal access to good education and the effectiveness
of policy alternatives. Provincial variation has been a consistent feature
of recent assessments of high school achievement in Canada over the
1990s. It is natural to ask to what extent provincial variation in school
inputs and the composition of student populations contributes to these
differences.
Objective
This paper adopts the decomposition technique of DiNardo, Fortin and
Lemieux (DFL, 1996) to decompose provincial differences in the distribution
of Programme for International Student Assessment (PISA) test scores
and assesses the relative contribution of provincial differences in
the distribution of "class size" and time-in-term, other school
factors and student background factors.
Findings
The study finds evidence that school factors did underlie observed
differences in the achievement distributions between Alberta and the
Atlantic provinces. More importantly, we find that removing differences
in the distribution of class size and time-in-term had a number of effects
depending on which province was being considered, the assessment being
considered and which part of the distribution. In some cases, the difference
in mean or median performance was not attributable to differences in
class size and time-in-term but this lack of noticeable effect masked
some noticeable effects in the different parts of the distribution.
In cases where differences in class size and time-in-term did contribute
to mean or median differences, it was not always, because the counterfactual
distribution was shifted entirely to the right. In many cases, the differences
in class size and time-in-term reduced the gap with Alberta in a particular
part of the distribution. An example was the reading assessment in New
Brunswick. Here, the analysis suggests that eliminating the differences
in class size and time-in-term would explain the gap in mean performance
but the proportion of students performing in the lowest reading proficiency
level would increase. Such an observation might be due to the way in
which New Brunswick schools optimally structure themselves to address
the needs of the local population. It also underscores the important
tradeoffs facing policy makers who seek to introduce reforms that improve
average test score performance. Such reforms may not benefit all students
equally and may even hurt lower performing students.
Data Source: The study uses the Canadian results from
the Programme for International Student Assessment (PISA) conducted
by member OECD countries in April and May of 2000.
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