Children struggle at school for many reasons, which could be one or overlapping learning difficulties: -- dyslexia, dyspraxia, dyscalculia, language and attention problems, etc.
Dyslexia was coined in German from dys- 'difficult' + Greek lexis ‘speech’, but it's a general term for disorders that involve difficulty in learning to read or interpret words, letters, and other symbols, but that do not affect general intelligence.
Dyspraxia is a problem of motor co-ordination. Children with dyspraxia have poor motor (physical movement) skills that are not in line with their other abilities or in keeping with what would be expected for their age. The child with dyspraxia has a difficulty with either or both of the following:
Gross motor co-ordination - this means difficulties in co-ordinating whole or large body movement, which are needed for many sports, especially ball games.
Fine motor co-ordination - this means difficulties in co-ordinating finger and hand movements that are needed for handwriting, drawing, eating and dressing.
Dyspraxia is sometimes also called nonverbal learning difficulty (NVLD), however, NVLD seem to imply a wider range of difficulties beyond motor - for instance, difficulties in understanding visual and spatial relationships which would, for instance, make it hard for children to do jigsaw puzzles, make sense of maps and draw their way out of a maze.
Dyspraxia can also be used as a term to describe some children who have a certain kind of speech difficulty. The child has unclear speech caused by difficulties in moving lips, tongue and palate in a co-ordinated way.
Specific language impairment
Children with specific language impairment have difficulty in understanding and using spoken language. These children will try hard to communicate with other by their eyes, finger pointing and other gestures and sounds instead of words. These children can be grouped according to whether they have receptive or expressive language difficulties. Receptive language refers to children's understanding of what is said to them. Expressive language refers to children's ability to speak to and to communicate with, others, children with either receptive or expressive difficulties will have limited vocabulary, and will usually find it hard to put words together.
Attention deficit with hyperactivity disorder
Attention deficit with hyperactivity disorder (ADHD) is a complex problem, its core difficulties are poor attention (or inattention), lack of impulse control (impulsivity), and hyperactivity. Inattention largely refers to the inability to keep 'on task', becoming distracted, and being unable to complete work in the classroom. Impulsivity describes behaviours where children can't stop themselves doing what they have the urge to do. Hyperactivity is 'overactivity', with children running around a lot, never sitting still, fidgeting almost all the time and flitting from one thing to another.
Dyscalculia simply means 'disorder of an ability to calculate'. Children with dyscalculia will do poorly at math, such as difficulty learning to count, difficulty in doing mental arithmetic, making error in simple written sums, slowness to learn times tables, etc.
Further reading: Dyslexia: A parents' guide to dyslexia, dyspraxia and other learning difficulties, by Dr Valerie Muter and Dr Helen Likierman