If children do not learn how to read in the first few years of primary school, they will struggle to complete the cycle, and are at greater risk of dropping out. It is therefore crucial to identify and test interventions that have the potential of making a large impact, can be implemented quickly, and are affordable to be taken to scale. This is the goal of the PRIMR Initiative in Kenya and the ToTAL program in Haiti--to test various options for improving learning outcomes and instruction in primary schools, using a randomized controlled design. Due to high student-teacher ratios, limited teacher training, and lack of sufficient text materials, reading outcomes for students attending Kenyan and Haitian primary schools are generally poor. There is international focus on improving literacy, including through bilateral donors such as USAID and DFID, in Kenya and Haiti. However, there is limited knowledge about how reading skills are acquired in multilingual environments such as in Sub-Saharan Africa or the Caribbean. This paper presents the findings of a longitudinal tracer study evaluating student literacy outcomes in Kenya over two years, three data collection points, and across two languages. Random selection and assignment methods were utilized to assign clusters of schools to a treatment and a control condition. The treatment group implemented a targeted literacy and numeracy instructional program. This paper also presents the findings of a two-year randomized control trial in Haiti evaluating the efficacy of a literacy curriculum for Haitian Creole and French. Both interventions included student books, teachers' guides, and ongoing teacher professional development and supervision. Analysis shows that PRIMR had a positive impact on the literacy outcomes of interest, including but not limited to letter sound identification fluency, oral reading fluency, the percentage of pupils who read at the MOE's benchmark, and reading comprehension, although not on all combinations of language, grade, and school type. The longitudinal analysis is able to determine how the language skills interact over time and across languages, and suggests that in some skills, pupils are transferring literacy skills from English to Kiswahili. This is unexpected based on the Western literature, which generally suggests language transfer in the other direction. Analysis similarly shows that ToTAL has a positive impact on key foundational skills of initial sound identification and letter sound identification, although not on all combinations of language and grade. Patterns suggest that instruction in the mother tongue of Haitian Creole led to gains in French on skills that were not explicitly taught. This research shows that teachers can be sensitive to in-service teacher professional development (ITPD) if that ITPD is closely linked to the books and lesson plans used in schools, and if teachers are observed and supported frequently.