This longitudinal study investigates negative transfer from L1 Dutch and L2 English into L3 French in the first three years of French education in a Dutch/English secondary immersion school. We focus on two word order constructions in declarative root clauses where the three languages differ: V-to-C movement (+Dutch, −French) and V-to-T movement (−English, +French). The results of a grammaticality judgement task and a gap-filling task show that the L3 learners transfer a large amount from L1 Dutch in the initial stages of the first year of French education followed by a dramatic decline in the second and third year of French education. At the onset of L3 learning, L2 English is less activated; however, its influence intervenes and stays stable in later years of learning.