In recent years, parastatal grain marketing boards have re‐emerged as important elements of grain markets in eastern and southern Africa, yet little is known about how farmers are responding to their scaled up activities. This article develops a conceptual model of farmers’ production decisions in the context of dual output marketing channels (government and private sector) when output prices at harvest time and the availability of one of the marketing channels are unknown at planting time. It then applies the model to the case of Zambia and uses nationally representative household‐level panel survey data to estimate the effects of the Food Reserve Agency (FRA), the government parastatal maize marketing board, on smallholder crop production and fallow land. The FRA buys maize from smallholders at a pan‐territorial price that typically exceeds market prices in major maize producing areas. Results suggest that increases in the farmgate FRA maize price raise farmer maize price expectations, which induces a supply response. Smallholders respond to an increase in the FRA price by extensifying their maize production. On average, a 1% increase in the FRA price is associated with 0.06% increases in smallholders’ maize area planted and quantity harvested. There is also some evidence that farmers reduce the area of land under fallow in response to FRA incentives but there is no evidence of reductions in the area planted to other crops.