This study revisits the existing scholarly debate on the possible impact of the principal's leadership on student achievement. Both `direct effect' and `indirect effect' models are discussed. A quantitative meta-analysis examines to what extent principals directly affect student outcomes. The small positive effects found in this meta-analysis confirm earlier research findings on the limitations of the direct effects approach to linking leadership with student achievement. Finally, lines of future research inquiry are discussed.
Key words: hierarchical linear model, multilevel research, sample designThe hierarchical linear model approach to a two-level design is considered, some variables at the lower level having fixed and others having random regression coefficients. An approximation is derived to the covariance matrix of the estimators of the fixed regression coefficients (for variables at the lower and the higher level) under the assumption that the sample sizes at either level are large enough. This covariance matrix is expressed as a function of parameters occurring in the model. If a research planner can make a reasonable guess as to these parameters, this approximation can be used as a guide to the choice of sample sizes at either level.Multilevel and, in particular, two-level designs are used frequently in educational and social research. Hierarchical linear models incorporating both random and fixed effects provide a useful statistical paradigm for situations where nesting is an obvious and direct consequence of multistage sampling as well as situations with nested sources of random variability. (See Bryk & Raudenbush, 1992, for a general introduction; see Raudenbush, 1988, for a review.) Some applications of such models follow.
In this article, we address the relationship between teacher expectation bias and student characteristics, its effect on long-term student performance, and the development of this effect over time. Expectation bias was defined as the difference between observed and predicted teacher expectation. These predicted expectations were estimated from a multilevel model in which teacher expectations of students' future performance in secondary education were regressed on students' prior achievement, IQ, and achievement motivation. Multilevel analyses were performed on a data set of about 11,000 students who entered secondary school in 1999 and who were monitored for 5 years. We found relationships between teacher expectation bias and student characteristics as well as a clear effect of expectation bias on long-term student performance. Teacher expectation bias partly mediated the effects of student characteristics on students' performance. Moreover, its effect was moderated by some of these characteristics. Mediation and moderation effects were the strongest for parents' aspirations. The effects of teacher expectation bias dissipated partly during the first 2 years but afterwards remained stable over time.
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