'A disorder of writing ability in which a learner has difficulty with letter…

Specific Learning Disabilities (SLDs) are neurodevelopmental conditions in which a learner of normal intelligence and adequate instruction struggles with one particular academic skill. Each SLD is named for the exact skill it disrupts: reading (dyslexia), written expression (dysgraphia), mathematical reasoning (dyscalculia), and motor coordination (dyspraxia).

The description in the question — difficulty with letter formation, spelling, and fine motor coordination specifically during writing — matches the defining features of Dysgraphia, the SLD that impairs the physical and cognitive processes involved in producing written text.

• Dyslexia is a reading-based disorder: it centers on decoding and fluently recognizing written words, not on the physical act of forming letters or handwriting mechanics.

• Dyspraxia is a broader motor-planning disorder affecting coordinated movement in everyday physical tasks generally, and is not defined specifically by letter formation and spelling difficulty.

• Dyscalculia involves difficulty with number sense, arithmetic, and mathematical reasoning — an entirely different domain from the writing-specific difficulties described here.

Therefore, the disorder described in the question is Dysgraphia.