This article describes data-based individualization (DBI) as a continuous process connecting assessment and intervention in mathematics for students with disabilities. DBI provides teachers with an evidence-based method for individualizing interventions for students who do not demonstrate adequate response. Assessment data gathered through the use of progress monitoring help teachers analyze and determine ways to modify components of intervention. DBI is an iterative process that involves: (1) adapting instruction using principles of intensive intervention and evidence-based practices; and (2) implementing these adaptations consistently and regularly. In this article, the authors provide a hypothetical example of how Mr. Drummond (a middle school special education teacher) used DBI to strengthen Molly's (a 6th grader with a specific learning disability) skills by intensifying her instruction within the multitiered system of support in place at Riverview Middle School. Mr. Drummond's approach to applying the principles of intensive intervention also illustrates how tracking student progress informs instructional decisions about the effectiveness of intervention adaptations. Many schools are using multitiered systems of support for students with mathematics disabilities (Gersten et al., 2009), so it is necessary for teachers to understand how to use DBI to create instructional programs that benefit individual students.