Secondary students with persistent mathematics difficulties need the most intensive intervention in order to improve their mathematics outcomes. One approach to intensifying and individualizing intervention is through data-based individualization (DBI). The present study used a single-subject, multiple-baseline-across-participants, replicated-across-skills design to investigate the effectiveness of DBI process on mathematics computation and mathematics concept and application performance of high school students who had intense needs in mathematics. Results suggest the interventions guided by the DBI process improved mathematics computation and mathematics concept and application performance of the participants. Implications of these findings and indications for future research are discussed.