We compare learning of two inflection types--obligatory noun plurals and optional noun possessives. We tested 107 Hebrew-speaking children aged 6-7 on the same tasks at the beginning and end of first grade. Performance on both constructions improved during this short period, but plurals scored higher from the start, with improvement only in changing stems. The main remaining challenge in mastering noun plural marking in grade school is thus to learn the various types of stem changes. In contrast, possessives improved across the board in first grade, with higher success on non-changing stems and first person suffixes respectively. This intense gain in first grade occurs when children learn to read and write and turn to the written modality as their main source of linguistic input. The study thus testifies to the impact of the shift from spoken language to the "language of literacy" on children's construal of Hebrew morphology.