This study explored how supervisory working alliance acts as a mediator between innovative instructional leadership and the effectiveness of schools, together with school environment as a potential moderator. This quantitative correlational study collected surveys from 259 public elementary school teachers across the Schools Division Offices of San Pablo City, Imus City, and Lucena City of DepEd CALABARZON. This study employed descriptive statistics, Pearsons r correlation, and multiple linear regression including mediation and moderation analysis. This study reveals that principals showed exceptional innovative instructional leadership and school effectiveness was evident according to the respondents. The supervisory working alliance received high marks as well. Both principal innovative instructional leadership and supervisory working alliance exhibited positive correlations with school effectiveness based on correlational analysis. Supervisory Working Alliance (SWA) partially mediated the effect of School Effectiveness (SE) on Principals Innovative Instructional Leadership Practices (PIILP), with a significant indirect path. School Environment (SEnvi) significantly moderated the PIILP-SE relationship, weakening the effect as SEnvi increased. This study concludes that the principals innovative instructional leadership significantly enhances school effectiveness when supported by supervisory working alliances and a favorable school environment. It is recommended that school leaders strengthen collaborative supervisory relationships and invest in sustaining the improvement of school effectiveness.