Effective extension systems are vital to smallholder agriculture. Education on sustainable management involves complex interactions and communication flows among information providers and practitioners. Farmer practice is often overlooked within extension knowledge systems, resulting in incompatible recommendations and barriers to sustainable agriculture. This study investigates the diversity of smallholder agricultural practices, with a focus on maize-legume systems in Tanzania, including seasonal cropping patterns and management, as well as linkages to extension recommendations and information flows. We used a mixed methods approach to assess the state of extension and farmer practice around maize-legume production in Tanzania. Household and plot-level survey data (n = 220) and focus group discussions (n = 5) and extension information was ascertained through interviews with key stakeholders (n = 12) and a survey of village-based extension advisors (n = 193). We found legume management practices were highly local. In the Southern Highlands for example, farmers produced from one to three bean crops per year, using a range of planting arrangements. Further, extension recommendations often did not take into account the varieties, fertilizer or plant spacing used by farmers. This comprehensive study of extension knowledge systems in Tanzania highlights the persistent disconnects that occur at multiple levels, acting as a barrier to sustainable intensification of smallholder farming.