Strength and Limitations
This study has both important strengths and some significant limitations. Strengths include
use of objective measurement of physical activity via accelerometry and observation of the
children’s physical activity during both the school day and the non-school period. Both
groups studied included diverse samples of children from multiple preschools. The major
limitations are associated with the cross-sectional study design. This design precludes
drawing a conclusion regarding a possible causal relationship between exposure to the
Montessori educational system and children’s physical activity. Further, because parents
self-selected one type of preschool or the other, we cannot preclude the possibility that intergroup
differences are explained in part or wholly by family characteristics rather than
characteristics of the school environment. Comparisons of the 2 groups of children were
adjusted for BMI, race/ethnicity, parent education and poverty index, so our findings should
not have been unduly influenced by these factors. However, it is possible that other
characteristics of the 2 sets of families, not measured in this study, could have affected our
findings. For example, we found that children attending the Montessori preschools were
more active than children attending the traditional schools during the non-school period as
well as during the school day. This could be explained by differences in the home
environments, and this was not examined in the present study. Further, this study did not
examine factors such as classroom and playground dimensions, and we recommend that
these factors be considered in future investigations comparing Montessori versus traditional
preschools.