Testing of previously studied information potentiates subsequent learning of new information, a phenomenon referred to as the "forward testing effect" (FTE). The current study aimed to investigate the developmental trajectory of the FTE and whether the reset-of-encoding process contributes to the FTE. Younger children, older children, and adults were instructed to study four lists of unrelated words, then either restudied or were tested following studying each of Lists 1-3, and took an interim test on List 4. Results demonstrated that interim testing on Lists 1-3 enhanced learning of List 4 for younger children, older children, and adults. Importantly, this enhancement varies with items' serial list position in both younger children and older children. Early List 4 items at list primacy positions benefited more from interim testing than later ones at non-primacy positions. Overall, this is the first study demonstrating that (1) the FTE generalizes to younger children, older children, and adults, suggesting the FTE emerges quite early in human life; (2) the reset-of-encoding process contributes to the FTE in both younger and older children.