Impaired ability to learn grade-appropriate mathematics WordNet 3.0 & Open English WordNet

Dyscalculia is a disability resulting in difficulty learning or comprehending arithmetic, such as difficulty in understanding numbers, learning how to manipulate numbers, performing mathematical calculations, and learning facts in mathematics. Wikipedia

Neurological condition, developmental or acquired Wikidata

Disability involving innate difficulty in learning or comprehending mathematics, in particular simple calculations. OmegaWiki

Pathology: difficulty with numbers. Wiktionary (translation)

A learning disability characterized by significantly below average mathematical ability. Wiktionary