As well as fixating and following along a line of text, children must also be able to make the fine adjustment needed to read to the end of one line, then accurately find the next one down to begin reading.
Our central and peripheral visual systems help control eye tracking. Our central vision processes what we are seeing in clear detail and defines what we are looking at. Our peripheral (or side vision) locates surrounding objects and lets us know where to look. In reading, the central vision processes the word, while our side vision locates the following word and tells us where to aim our eyes next.
Unlike convergence and accommodation which develops very early in an infant’s life (e.g., crawling), fine eye tracking skills do not actually mature until they are around 5 years of age. As developmental milestones, some children may take longer until they learn these skills. However, if they do not track well by the time they are 7 years old, this is when reading may be affected.