This dissertation research was grounded in a sizable body of research on identification of students who are gifted, who have specific learning disabilities (SLDs), and who are both gifted and have SLDs, which is referred to as twice exceptional. Four groups of students were compared: those who are gifted with SLDs, those who are gifted without SLDs, those who are average with SLDs, and those who are average without SLDs. Study 1 compared groups two at a time on their learning profiles (achievement on normed measures of reading, writing, and oral language) and their phenotype profiles (normed measures of working memory components supporting learning). Study 2Examined whether each of these groups responded differently to computerized instruction for reading and writing, which is referred to as response to intervention (RTI). Prior research showing that twice exceptional students may score higher on learning profiles but not on phenotype files when compared to average students with SLDs was replicated. A new finding was that gifted students without SLDs achieve at level commensurate with their verbal giftedness but twice exceptional achieve at average level on learning profiles. Comparison of learning and phenotyping profiles was more informative than the RTI approach for group data. The conclusion is that flexible approaches are needed to identify SLDs, both in those who are and are not gifted. These approaches should consider normed measures of reading and writing achievement and phenotype measures of the biological bases of SLDs. Additionally, teacher and parent reported current and past learning histories and response to classroom instruction should also be considered in planning, implementing, and monitoring instructional programs for all students.