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Investigating the Dimensions of Spelling Ability

In this study, the latent structure of a spelling achievement test for elementary school grades was investigated. Factor analyses revealed that for Grades 2 to 6, the test was unidimensional, whereas for Grade 1, two factors were found: a phonological factor and an orthographic factor. Because of the anchor-test design, vertical equatingwas required to fit a two-parameter, unidimensional item response theory model. Concurrent calibration of the parameters, implemented in BILOG–Multiple Groups (MG), was used as the linking procedure. An evaluation of the model showed that invariant parameter estimates and ability scores were obtained. The transition from an alphabetic to an orthographic strategy occurs in the first grade. Learning to spell throughout elementary education mainly consists of learning to apply orthographic knowledge.