This study was conducted to examine the differences in high school biology achievement and student affect towards teacher and content from the use of individualized correctives as part of mastery learning. An experimental pretest-posttest with control group design was used during the fall 2011 semester. Over a thirteen-week period, 99 students in five general-level biology classes received mastery learning instruction covering several state standards. Of the 99 students, 50 received individualized correctives based on the results of formative assessment. The other 49 students received a non-individualized study guide after the formative assessment. A written summative examination was used to measure achievement. The Instructional Affect Assessment Instrument (IAAI) was used to measure student affect. The written summative evaluation and the IAAI were administered as a pretest to assure the independence of the covariate and treatment effect. Data were analyzed with a multivariate repeated measures test and ANCOVAs. No differences were found between the individualized corrective group and the general study guide group in terms of achievement or student affect toward content or teacher. Results indicate that individualized correctives were not the key factor in mastery learning for this population and type of science content. Further study on the impact of individualized correctives in different subject areas and populations is recommended as well as additional research on the effect of repeated testing. [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.]