Tanzania receives significant development and public sector investment, but robust accountability systems are weak, and communities rarely have a means through which to hold duty-bearers responsible. This reduces the effectiveness, impact and value for money of these investments. Funded through UK Aid from the UK government, the four-year Social Accountability through Youth (SAY) project empowers young people and marginalised groups to monitor projects in their communities. Using our technical partner Integrity Action’s DevelopmentCheck app, young people identify challenges and work with other community members, implementing actors and authorities to discuss and fix these problems. Now in its final year of delivery, the project’s 358 Community Monitors (CMs) and 36 Youth Cluster Coordinators (YCCs) have so far identified 3,961 problems and worked with their community Joint Working Groups to resolve 3,041 of these (a 77% Fix-Rate), benefitting over 750,000 people and increasing the effectiveness of projects totalling more than £15 million. The project’s 14 SAY Campaign Coordinators have increased knowledge of social accountability mechanisms across a further 1,241 communities, with individuals in 30 of these now also monitoring their community projects. A recent evaluation of SAY indicated that 99% of the young people engaged feel they are role models for their peers and believe they are generating increased impact in their communities, while there has also been a significant shift in the way community members perceive and interact with youth.