Parents who feel disappointed at their teenagers' failure to pay attention in class, and inability to sit quietly long enough to finish homework or plan ahead, should take _ . Their children are not being lazy or careless, according to new research. The research has found that teenagers' brains continue developing far longer into adulthood than we used to think. Teens may look like young adults but their brain structure is similar to that of much younger children. "It is not always easy for teens to pay attention in class without letting their minds wander, or to ignore distractions from their younger brothers or sisters when trying to solve a maths   problem," said Dr Iroise Dumon-theil. "But it's not the fault of teenagers that they can't pay attention and are easily distracted. It's to do with the structure of their brains. Teens simply can't think as well as an adult." The research showed that the brain of a teenager works less effectively than that of an adult. "We knew that the front of the brain of teens functioned in a chaotic    way but we  didn' t realize it continued until the late 20s or early 30s," said Dr Sarah-Jayne Blakemore, who led the research. Chaotic thought patterns are a result of teenagers' brains containing too much grey matter -- the cell bodies and connections which carry messages within the brain. As we age, the amount of grey matter in our brain reduces. "What our research has shown is that there is simply too much going on in the brains of teens," said Blakemore. "The result is that their brain energy and resources are wasted and their decision-making process is badly influenced. Adults, on the other hand, have less grey matter. This means that the brain works far more effectively." What's the text mainly about?
Teens have different brains from those of children. Adults work more effectively than teens. Grey matter makes teens unable to pay attention. Brain energy is wasted in the brain's activity.