This article aims at a deeper understanding of the importance of native languages in education and development, with Haiti as a case study. About half of Haiti's population is illiterate. Among ten children who enter the first grade, at most one (10%) will graduate from high school; a large proportion will drop out of school at an early age. Language is a factor in such academic failure. Education in Haiti is carried out mostly in French, which is spoken fluently by at most 5% of the population, while the language spoken by 100% of the population, namely Haitian Creole (Kreyòl), is by and large excluded from the school system, in spite of legislation, official curricula, and various efforts from civil society to generalize the classroom use of Kreyòl. We hypothesize, based on comparative research on education in the mother tongue, that the systematic classroom use of Kreyòl-at all levels, but especially in early grades-promotes academic success in Haiti, as illustrated in this paper. This article reports on the results of an intervention to improve early-grade reading and writing in Haiti. This intervention is part of a larger project titled "Mother-Tongue Books: Learning to Read in Haiti" (MTB) with Christine 2 of 56 W. Low as principal investigator. The project promotes the collaborative production of books by Haitian school children in their native Kreyòl and the use of these books to enhance literacy gains in early grades. An assessment carried out during academic year 2012-2013 (DeGraff 2013b), using the Early Grade Reading Assessment (EGRA) instrument, showed that the first and second graders at Lekòl Kominotè Matènwa (LKM) in La Gonâve, Haiti, performed at a much higher level than their counterparts in five schools nearby. LKM is a pioneering MTB school where Haitian Kreyòl is used as the primary language of instruction. These initial results (referred to below as the "baseline assessment") spearheaded our intervention, whereby the MTB approach was introduced to the five other schools in the study. The final EGRA evaluation data show that the students in the five non-LKM schools, through the MTB intervention, substantially reduced the gap in their reading-and-writing levels vis-à-vis their LKM counterparts. In other words, the literacy skills of the students at the five non-LKM schools rose nearly to the level of those at LKM through the use of an intervention based on child-centered active-learning pedagogy with the systematic use of their native Kreyòl. In this paper, we analyze the data collected in the course of this project and their implications for policies to enhance reading and writing instruction in Haiti.