Engaging underrepresented populations of women and minorities in Computer Science (CS) represents our greatest untapped resource for increasing the STEM workforce. In recent years, tremendous efforts have been geared towards developing learning materials to increase the interest of underrepresented students in CS. More recently, CS education researchers are beginning to recognize the need to apply the learning sciences to develop age- and grade-appropriate curricula and pedagogies for developing computing competencies among children. One effective approach to build learning competencies among young underrepresented students is through Collaborative Learning, which is an educational approach that involves groups of learners working together to solve a problem or create a product. Our goal, in this paper, is to report our experiences on designing and delivering a curriculum that teaches programming to middle school students using App Inventor through collaborative learning. Our curriculum is developed on the hypothesis that visual programming environment, in this case, App Inventor, present an alternative way of learning programming, which in the collaborative learning environment can enhance programming competencies and interests in underrepresented students. In this experience report, we will describe how we implemented this curriculum as a block course; present our lessons learned, and few findings from the evaluation.