Virtual instruction and blended learning are two of the fastest growing learning modalities in K-12 education. Blended learning is a formal education program in which students learn at least in part through online learning with some element of student control over time, place, path or pace and at least in part at a supervised brick and mortar location away from home. The purpose of this study was to determine the effectiveness of blended versus virtual instruction on 9th grade students' academic achievement/growth in English language Arts classrooms using the students' Common Formative Assessment scores. The data from this study was used to determine if there was a statistical significance on student achievement using the students' fall, winter, and spring Common Formative Assessment scores to assess academic performance. The data compared students' academic performance in a virtual and blended learning environment. The study considered outcomes for all 9th graders as well as for subgroups of gender and Individualized Educational Plan (IEP) status. To allow for statistical control, only the assessment scores of the students who were in the virtual environment in the fall and moved to a blended environment were compared to their winter and spring scores, which meant the data of the same students were used throughout the study. The participants for this study included 2,433 9th grade ELA students from a Southwest Tennessee urban school district. A repeated measures analysis of variance was conducted to determine the impact of virtual versus blended instruction on 9th grade ELA students' growth/achievement on fall, winter, and spring Common Formative Assessment scores for district assessed standards. The quantitative data showed there was a significant statistical difference in students' growth/achievement when engaging in a virtual versus a blended learning educational environment this was also found to be true based on students' gender and IEP status. Also, while it was hypothesized students would demonstrate improved academic performance once returned to the in person blended learning environment; students demonstrated a regression of academic growth/achievement. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]