This paper analyses the process of implementing a just-in-time (JIT) methodology in maquiladora assembly plants in Mexico, through 20 activities undertaken in the areas of administration, supervision and production. The proposed approach uses a factor analysis of each group of variables (validating their feasibility through an analysis of the correlation matrix) by sections, activities and benefits obtained. A structural equations model is proposed to show how key factors in the success of the implementation of JIT associated with productive activities interrelate with factors linked to benefits. The results forthcoming from the study show that the benefits obtained through the proper administration by senior managers of their powers are directly reflected in the plant's productivity indices, such as increases in output, quality and the operational flexibility of production systems. Furthermore, a good relationship with and management of suppliers guarantees an acceptable level of control over inventories, regarding both work in process and the end product, and likewise impact upon productivity indices.