Before we get to formal decision making in adolescents, a little bit of (simple!) neurobiology.
At around the age of seven there is a growth spurt in human brain development. This is mainly in the left hemisphere, which gives us entry into the world of intellect, logic and reasoning.
From 15 to the mid-20s, an area known as the prefrontal lobes begin to develop and function. We now know that these areas are involved in future planning and long-term risk assessment.
The implications of this knowledge in relation to decision making in adolescents is enormous. Firstly, we shouldn't expect young children to make rational decisions. They simply don't have the hardware. It's not until sometime after seven do they begin to do abstract thinking, because at this stage the hardware that does abstract thinking becomes prominent.
If your teenager has ever done something you consider stupid, and your reaction was 'What were they thinking?' Well, the answer is they were thinking about doing that thing and the associated pleasure. They were not thinking long-term, nor considering the risks. Again, the hardware, the prefrontal lobes, simply isn't functioning yet in a way that allows them to consider the long-term consequences of their actions.
So a small child is not simply a miniature adult. There are many phases that they go through in terms of their brain development, and each phase has to finish before the next one starts. Each stage needs different kinds of input so the child is stimulated in a way that allows the nervous system to develop normally.
If a child receives stimulation that its brain is not ready for, it somehow impedes the growth of the part of the brain that should be stimulated. And they may need to catch up later, (if that's possible).
It also means that those troublesome teenage years (usually!) pass as the brain begins to shift its focus of activity. Instead of being run by their emotions, you could say, the emotional decision making in adolescents begins to be tempered by the prefrontal lobes, the area where decisions about right and wrong and cause-effect relationships are dealt with.
So this is a quick run through some developmental neurobiology, the growth of the 'hardware'. So what about the 'software', what are the challenges to making healthy decisions in adolescents?