In this paper we first review the main results in the theory of schemata in Genetic Programming (GP) emphasising their strengths and weaknesses. In particular we summarise a new schema theory we have recently developed for GP with one-point crossover and point mutation which is based on a definition of schema quite close to the one used in genetic algorithms. Then we study the creation, propagation and disruption of this new form of schemata in real runs, for standard crossover, one-point crossover and selection only. Finally, we discuss these results in the light our GP schema theorem.