The underbelt, colored belt, ranks are called kyu grades. Every successive test becomes more difficult. At the early tests most schools allow a student an opportunity to do a skill or a kata over again if they made a mistake to prove that they know the material. The higher one rises in rank the more difficult the test. The higer the rank of the test the fewer mistakes, bad stances and the like are tolerated. At that point if people are passing tests with lots of mistakes I would find another school.