This paper discusses the concept of Instrumentation-Based Validation (IBV): the use of model instrumentation and coverage-based testing to validate models of embedded control software. IBV proceeds as follows. An engineer first formalizes requirements as assertions, or small models, which may be thought of as monitors that observe the behavior of the controller model as it executes. The engineer then instruments the model with these assertions and develops test suites with the aim of highlighting where assertion violations occur. To make our discussion of IBV more concrete, we also consider its implementation within the Reactis tool suite for the automated testing and validation of controller models given in ^® /Stateflow^®.