The theory, implementation and understanding of how children develop is frequently based on the work of Jean Piaget, who is regarded as the father of developmental psychology. Piaget's cognitive developmental theory hypothesised about 'when and how children think and how their thinking changes as they mature'. This theory implies that there is a predetermined growth rate for physical and cognitive functions which explains why some children have a delay in a particular ability or skill such as speech or motor skills. Children who have poor neuromuscular development and poor physical co-ordination due to cerebral palsy, or those with dyslexia and dyspraxia, may have long-lasting and persisting difficulties with skills including fine and gross motor skills. Others have oral and written language skills deficits. The Disability Discrimination Act 1995, which has been amended to the Special Educational Needs and Disability Act 2001 (SENDA), had a profound influence on effective provision for those with disabilities such as dyslexia.