This quasi-experimental mixed-methods study investigated how integrating language arts and visual arts with history instruction affected high school English as a Second Language (ESL) student achievement and integrative thinking ability. This study had three objectives: (a) to collaboratively develop and implement a curriculum that integrated language arts and visual arts with history; (b) to measure that curriculum’s impact on student achievement and integrative thinking ability; and, (c) to explain that impact. Two integrated units of instruction were developed by a team of four high school teachers representing three disciplines: history, English to Speakers of Other Languages (ESOL), and visual arts. The integrated instruction, which in this study was the intervention, was then implemented in the ESOL teachers’ classes. The comparison group consisted of students in other sections of the same ESOL teachers’ classes. The researcher collected, processed, and analyzed work samples, focus group interviews, grade data, state standardized test (SST) scores, World-Class Instructional Design and Assessment (WIDA) scores, and participants’ scores on the Evaluation of the Potential for Creativity (EPoC) assessment for measuring integrative thinking. The null hypothesis of the primary question is: There is no significant difference in performance on the EPoC instrument between the comparison and intervention groups. In addition to EPoC, other student achievement data was analyzed. Students in the integration group performed better on the instruments measuring other achievement data in English and history, but not significantly. However, the entire sample performed much better than the rest of the district and state. Collaboration may have contributed to the participants’ relatively high achievement. This study may inform school leaders and guide curriculum design at the site, as well as lead to larger studies to determine the effects of implementation of integrated curricula on secondary students.