This critical ethnographic case study explores the impact of Performance-Based Assessment Tasks (PBATs) on high school dynamics and instructional practices, particularly in schools serving immigrant communities. PBATs, considered alternatives to standardized testing, have shown promise in enhancing student engagement, critical thinking, and college readiness. Drawing on interviews and fieldwork at four International High Schools, the study investigates how PBAT adoption influences day-to-day operations, teacher-student interactions, and school culture. Results reveal that PBAT implementation requires early investment in skill development and mentorship, transforming educators into facilitators and students into active learners. Moreover, the oral presentation aspect fosters multilingual proficiency. Despite challenges, PBATs offer a pathway to equitable assessment practices and educational transformation. Framed within a justice-oriented framework, this research highlights the potential of PBATs to create inclusive and empowering learning environments for immigrant and marginalized students.