In West Africa, farmers face challenges to innovate and change their practices toward more sustainable cropping systems. Farmer Field Schools (FFS), an advisory service based on participatory principles, aim to support farmers' innovation. This study investigates farmers' innovation by characterizing their trajectories of change in agricultural practices after they participated in FFS. Two contrasting types of FFS for family farmers in the cotton-growing area of West Africa were selected. The FFS differed in how they were implemented; farmer participation was either consultative (farmers participated little in developing the FFS curricula and structure) or collaborative (farmers participated actively in developing the FFS curricula and structure). Former FFS participants were interviewed on their successive changes in cropping practices over a 4 to 8-year time span. The sample included seven FFS on rainy season cropping (17 interviews in Burkina Faso, 22 in Togo), and four vegetable gardening FFS (21 interviews in Togo). The Efficiency-Substitution-Redesign framework was applied to pest management, organic and mineral fertilization and legume cropping practices. Our results show that the way FFS were implemented influenced farmers' trajectories of change in practices. After consultative FFS, changes in practices were limited. After collaborative FFS, we found a variety of changes in the production and use of compost, biopesticides, and inclusion of legumes in the cropping system through intercropping or pure cropping. Redesign of cropping systems included increasing on-farm compost production, collective pest management, and crop rotations. Collaborative FFS can be seen as step-by-step design processes for locally adapted cropping systems. This is the first time that farmers' trajectories of change in practices are used to assess the effects of FFS. This approach is valuable for understanding farmers' decision making and the role of participatory innovation support