Acknowledgments
All the opinions expressed in this work are those of the authors.
Note
1We examined the pretest results for which we were unable to gather a matching posttest, and
compared this pool of absent or otherwise attritted students with the analysis sample’s pretest scores using
pooled-sample t-tests. For the 1998–1999 school year implementations, there were no significant
differences or trends between the analysis sample and the dropped sample on total pretest score. For the
1999–2000 and 2000–2001 curriculum implementations, analysis of the missing data did indicate some
differences between the analysis sample and the students for whom no posttest was collected. In general,
and not surprisingly, the analysis sample slightly outperformed the dropped students on the pretest
measures, suggesting that the students included in the results were better prepared academically than those
who were dropped. The effect sizes, however, were relatively small, averaging only .25. The difference
between the analysis sample and the dropped sample does not directly affect the paired-sample analysis, but
it may have an indirect effect in that for our sample, better prepared students tend to show slightly lower
gain scores (r¼.18, p