The study examined the contributions of "orthographic processing" factors to the spelling achievement of typically developing middle-elementary students. The researcher framed orthographic processing as a multilinguistic, multidimensional construct involving process factors related to procedural orthographic operations and product factors related to declarative orthographic knowledge. Accordingly, the basic correlational design analyzed data related to phonological awareness, orthographic coding, word-specific (lexical) orthographic knowledge, general (sublexical) orthographic knowledge, spoken morphological awareness, receptive oral vocabulary, and the composite predictor variables of declarative orthographic knowledge and orthographic processing. The researcher and two trained assistants collected the data from a convenience sample of 59 fourth and 71 fifth grade students from three research sites in southeastern Wisconsin using a battery of standardized and experimental tasks. Overall spelling achievement measured with a norm-referenced assessment and multilinguistic spelling achievement assessed with a multilinguistic, prescriptive spelling instrument functioned as the dependent variables. Pearson product-moment correlation analysis disclosed significant relationships among all research variables including a strong relationship between the two dependent variables. Hierarchical multiple regression analyses indicated that orthographic processing, orthographic coding, declarative orthographic knowledge, and word-specific (lexical) knowledge predicted unique variance in overall spelling achievement and multilinguistic spelling achievement. The largest significant contributions occurred when orthographic coding, word-specific (lexical) orthographic knowledge, and general (sublexical) orthographic knowledge entered the regressions as separate predictor variables. In addition, spoken morphological awareness contributed unique variance to spelling achievement in five out of six of the regressions. Phonological awareness contributed significant unique variance to multilinguistic spelling achievement only when regressed with orthographic coding, word-specific (lexical) orthographic knowledge, and general (sublexical) orthographic knowledge. Further, the findings indicated that middle-elementary students drew upon phonological, orthographic, and morphological linguistic processes while spelling, consistent with the repertoire theory of spelling. Thus, the implications of the study suggested that spelling instruction and assessment should address the multidimensional nature of orthographic processing within a multilinguistic framework. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]