Age is a determining factor of the normal attention span in babies, children and adults. A child's attention span generally gets longer with age, and by the time he or she reaches his or her late teens or early 20s, a normal attention span is 15 to 20 minutes. Activities also can affect attention spans. Attention is held for longer periods by people who are taking part in activities that interest them.

Babies are born with a short attention span that is held only for a few seconds for about the first 10 days of life. Development of the attention span differs in children after this period. Babies often develop longer attention spans by staring into the face of their parents or caretakers for varying amounts of time. During the first year of life, each baby is different, with some having short attention spans of a few seconds and others maintaining attention for minutes on a single activity. Either type of attention span is considered normal in babies.

Children who are attending school develop a longer attention span through the activities typically completed in an educational environment. Girls usually are equipped with longer attention spans than boys during their school years. Older students continue develop longer attention spans as they are provided with new experiences and activities.

Factors that can affect the development of a normal attention span include learning difficulties throughout childhood. Medical conditions that affect the attention span include attention deficit disorder (ADD) and attention deficit hyperactivity disorder (ADHD). Attention can be affected when the focus of the child or adult is placed on small, insignificant details or by the general restlessness caused by ADD and ADHD.

Technology can have a negative effect on attention span, even in adults. In some cases, the large amount of information that is available on the Internet can reduce an adult's normal attention span to less than 60 seconds as he or she surfs from website to website. Extreme cases of Internet addiction can reduce the attention span of an adult to less than 10 seconds.

College students have an average normal attention span of 15 to 20 minutes. Lectures and classes are commonly 50 to 75 minutes long and require being broken up into smaller sections to maintain the attention of average students. These short segments can be be interspersed with short activities, during which the attention is focused on the activity before being brought back to the lecture or class when the activity is over.