Final answer:
Percy's ability to achieve high grades is negatively affected by dyslexia, which hinders reading ability, and dysgraphia, which makes writing a challenge.
Step-by-step explanation:
Percy faces significant challenges due to two prominent learning difficulties: dyslexia and dysgraphia. Dyslexia is a learning disability that impairs a person's ability to process letters and words, commonly resulting in difficulties with reading, which is essential for most academic tasks. Dysgraphia is another learning disability that results in a struggle to write legibly, making the physical task of writing extremely challenging for individuals with this condition. Both of these can impede the ability to achieve high grades, as success in school often relies heavily on the ability to read and write efficiently.