Low-income students from underrepresented communities experience significant educational inequalities, including chronic absenteeism, mental health crises, trauma exposure, and social injustices. These conditions escalate risks of dropping out and justice system involvement. Middle-school youth must navigate intense social and emotional change. To address such challenges, The Arthur Project (TAP) provides intensive, in-school, therapeutic mentoring and family support. The program teaches students essential life skills, such as problem-solving, communication, and academic engagement. Students are empowered to strengthen their resilience, perseverance, self-actualization, and confidence. TAP provides up to 500 h of therapeutic mentoring yearly over three years, delivered individually and in small groups by social work interns. The research question was as follows: Does structured, intensive in-school therapeutic mentoring with social work interns increase the socioemotional, cognitive, noncognitive, and academic skills and engagement of underserved middle-school students? This evaluation for the school year 2022–2023 is based on the program of 200 students and 30 mentors, with quantitative mentee, mentor, teacher, and caregiver surveys and qualitative interview data. The program and evaluation methodology are described, with results and conclusions. Students showed significant improvement in all domains; mentors reported student increases in confidence, perseverance, problem-solving, and communication; and teachers and caregivers reported students’ increased academic engagement. The Arthur Project program can become a national middle-school mentoring model to address widespread student inequalities.