The integration of the generate-and-test paradigm and semi-rings for the aggregation of results provides a parallel programming framework for large scale data-intensive applications. The so-called GTA framework allows a user to define an inefficient specification of his/her problem as a composition of a generator of all the candidate solutions, a tester of valid solutions, and an aggregator to combine the solutions. Through two calculation theorems a GTA specification is transformed into a divide-and-conquer efficient program that can be implemented in parallel. In this paper we present a verified implementation of this framework in the Coq proof assistant: efficient bulk synchronous parallel functional programs can be extracted from naive GTA specifications. We show how to apply this framework on an example, including performance experiments on parallel machines.