A study to determine the impacts of farmers field schools (FFS) on smallholders’ adoption of good agricultural practices in tea and to assess sustainability of smallholder tea production was conducted in the highlands of Kenya. Input-output data on tea management and on sustainability indicators (score 0-10) were collected from a sample of 120 FFS participants at the beginning of the study and from 60 randomly selected FFS participants and a comparison group of 60 non-FFS participants at the end of the study, 18 months later. The study showed that the smallholder tea systems are moving towards social sustainability and economic returns were positive. Sustainability indicator scores, for FFS members, increased by 4% from the base period. The FFS participants also attained a significantly higher level of farm sustainability, knowledge gains on good agricultural practices (GAP) and higher yields and farm and tea income than their non-FFS counterparts. These findings indicate that FFS methodology had a positive contribution to enhancing farmer learning and adoption of good agricultural practices in tea and improved farmers’ livelihoods.