After turning 4 years of age, Yamato applied for entrance to the academy for formal Samurai training, which was why he was called for a test to the academy grounds. When he arrived to the place for his test all the other examinees where suprised that such a young boy was there to give the test which made a few of them smile in derision.
The test wasn't hard at all as the requirements weren't high atleast in the academic part anyways as children just need to know basics like elementary language and elementary maths but that's where the easy part ends as passing the written exam wasn't enough to enter the samurai academy as the chakra test was the most important part, this part involved an examiner injecting a small wisp of chakra to activate the chakra coils of children.
If a child has potential to use chakra then the wisp of chakra will be able to make a full circulation in the body of the child before being absorbed and if a child doesn't have potential than the circulated wisp will be comeback to the examinar or if there is any problem with chakra coils with the child than the chakra will not be circulated properly.
A big number of children donot pass this test as they don't have the potential to use and store chakra but this is not the end of the road for them as they still have the chance if they pass the third test. The third test is a physical test that guages the physical abilities of the children which is what the children are told but there is more to it, atleast for the children that didn't pass the second test as it not only test the physical condition of the children but also the will of those who didn't paas the second exam but still want to become samurai.
Unlike shinobi where ability to wield chakra is of paramount importance becoming a samurai doesn't need chakra as being a samurai is more of a way of life than a profession. Yes the path ahead without chakra will be extremely hard but there is still a way for there for those who have the will to strive for it.
Yamato passed the first and third exam topping them both while he didn't need to go through the second exam as he had samurai parents, children with samurai parents or guardians don't need to go through the second exam because the parents/guardians can determine the fact that their children can wield chakra or not, they just have to report it to examinar.
During the second test a pair of identical twins caught his eyes as among the children that didn't pass the second test the twins were also the ones who didn't pass but unlike the others they weren't disappointed but rather they looked extremely determined and fired up which was reflected during the third test as they were one of the few to go past their limits to complete the third test.