"The presence of peers makes adolescents and youth,but not adults, more likely to take risks," Steinberg and Gardner concluded.

In a 2005 study, psychologist Laurence Steinberg of Temple University and his co-author, psychologist Margo Gardner, then at Temple, divided 6 people into three age groups: young adolescents, with a mean age of 14; older adolescents, with a mean age of 19

Steinberg and Gardner randomly assigned some participants to play alone or with two same-age peers looking on.