The Kirigakure ninja academy in terms of graduates splits up each students into particular specialties after their first year based on their observed aptitudes, temperament and affinity. There are five courses that are considered their unit, which are also divided up into two different companies based on the role in combat that person is expected to take.
The companies are Combat Company and Support Company. While there is some variation based on individual years there’s always roughly half the students in each. Most of the students in support company are students who do not show any obvious aptitude in one course, and are considered basic students, which means they will get basic training in all courses overall. Students in the basic course can advance to a standard course if they show progress but that’s very rare. The other part of support company is the Genjutsu standard unit, despite genjutsu’s use in combat it’s considered one of the soft arts and thus more suited to support.
Minami has a lot to say about being pushed into there.
The other three units are all a part of combat company, they are Kenjutsu, Ninjutsu, and Taijutsu. Despite Kirigakure being known for it’s swordsman, taijutsu is the largest standard unit by far as a specialty for combat company. Given someone in the kenjutsu unit may also be put into the taijutsu unit as well to make them more rounded as a close range fighter, though they have to be fairly adept to do so since most students if they are put into a standard course are only ever put into one. Ninjutsu is the smallest course in combat company because it’s a course that requires both good chakra control and good reserves to be effective in which is a rare combination with the fact that most the academy ninja come from common stock (genjutsu company is usually good chakra control with average or lower than average reserves).
In terms of gender, support company has more girls then boys and en vice versa. This is partially because company placement is partially based on temperament with boys being expected as more aggressive than girls in combat, partially it’s because males are naturally stronger than females, and partially it’s because girls are traditionally in support roles.
Ume probably would have been put into basic course if she wasn’t both very aggressive in fighting during her first year and also wind natured which favors itself to fast movement. Her nature was also factored into her being put into kenjutsu, though the real kicker was because she was so much smaller than the other kids they gave her a sword to improve her reach.
No matter what company you’re from, it’s considered very unlikely that you’ll make it to full shinobi. In fact only about four of the characters who are active in story would have likely passed the graduation, and despite her skill Ume isn’t one of them. Only ten percent successfully become genin, the other ninety percent are sent to other more specialized companies which are Infiltration, Medical and Garrison. The Garrison company is the biggest because it serves as the military police for the entire country, acts as border patrol as well as shipping patrol for pirates and during war as shock troops for most operations. It’s the only company that draws from both Support and Combat company. Infilitration and Medical both exclusively draw from Support company because the last six months of training focus more on noncombat skills for support company than not. It’s part of this that makes it so only a third of full shinobi in Kirigakure are part of support company.
Anbu is a special case because any person whether full shinobi or not who has received academy training can apply to become anbu. It doesn’t mean they’ll succeed the intense training and be fully accepted, but because of the nature of anbu work they never limit who can apply to become part of the ops making it the only truly equal opportunity job for academy goers in Kirigakure.