The Girl Scouts of the USA have six levels: Daisy, Brownie, Junior, Cadette, Senior and Ambassador. Girl Scouts moves or "bridges" to the next level, usually at the end of the school year, when they reach the age of advancing. The Ambassador level is the most recent, having been added in 2011.

Daisy is the initial level of Girl Scouting. Named for Juliette "Daisy" Gordon Low, they are in kindergarten and first grade (around ages 5–7). They meet in minimally groups of five girls with two adult leaders who help the girls plan activities to introduce them to Girl Scouts.

Brownies are in second and third grades (around ages 7–9) and earn triangular shaped Brownie Leadership Journey Awards and National Proficiency Badges.

Juniors are in fourth and fifth grades (around ages 9–11). Their uniform is a green vest or sash which may be worn with a white shirt and khaki bottoms. They work on badges and fun activities.

Cadettes are Girl Scouts who are in sixth, seventh, and eighth grades (around ages 11–14). Their uniform is a khaki vest or sash with white shirts and khaki bottoms. They earn diamond shaped badges.

Seniors are Girl Scouts who are in ninth and tenth grade (around ages 14–16). They wear the same uniform as Cadettes and earn rectangular shaped badges.

Ambassadors are Girl Scouts who are in eleventh and twelfth grade (around ages 16-18). They wear the same uniform as Cadettes and Seniors. They earn badges that are shaped like an octagon.

More Info: en.wikipedia.org