In this paper, we consider mathematical competitions for pre-university students, such as the "International Mathematical Olympiad" (IMO) and many national and regional Olympiads following a similar model. The problems proposed in these contests must be solvable by 'elementary' methods (i.e., without using calculus) and belong traditionally to four areas, namely, algebra, combinatorics, geometry, and number theory. Usually there is no explicit curriculum prescribing what parts of these subjects may be involved in the problems, however there is a "hidden curriculum" (HC) that may be deduced from the problems proposed and from what is considered a complete solution. In this paper, we try to characterize this HC showing typical problems, subjects, solutions, and strategies for each of the main areas. We also make a comparison of the HC with the traditional secondary school curriculum (SSC), with the following two goals: (1) to identify the main points that should be addressed in the preparation of students aspiring to participate in mathematical competitions, and (2) to suggest possible changes to it and diminish the gap between school and contemporary mathematics.