Dyscalculia is a specific and persistent difficulty in understanding numbers which can lead to a diverse range of difficulties with mathematics. It will be unexpected in relation to age, level of education and experience and occurs across all ages and abilities.  (BDA definition)

Hertfordshire's definition for Developmental Dyscalculia

Developmental Dyscalculia will be distinguishable from general mathematical difficulties due to the severity of difficulties with:

• number sense: the ability to understand and use numbers and the number system (i.e. ordering);
• subitising: instant recognition of the number of items in a small group without counting;
• symbolic and non-symbolic magnitude: ability to discriminate quantity pictorially or in symbols (i.e. maths words and digits).

Dyscalculic learners may:

• have difficulty understanding simple number concepts;
• lack an intuitive grasp of numbers;
• have on-going problems learning number facts and procedures, performing fluent calculations, and interpreting numerical information.
  
  Even if they produce a correct answer or use a correct method, they may do so mechanically and without confidence.

Developmental Dyscalculia is:

• a persistent difficulty in understanding and acquiring skills related to arithmetic and basic number sense despite targeted intervention;
• an unexpected difficulty in maths that cannot be explained by external factors;
• diverse in character and occurs across all ages and abilities;
• a specific learning difficulty for mathematics, especially arithmetic;
• often co-occurring with other learning difficulties and neuro-developmental difficulties.

An assessment of developmental dyscalculia is a process, not an event and should happen over time, taking into account a child/young person's patterns of strength and needs through the assess - plan - do - review cycle.