Many techniques have been developed to explain logical reasoning, such as proofs or abduction. However, such methods are useful mainly for experts in logic, e.g., for debugging ontologies. For actually explaining logical consequences and missing consequences to end users of logic-based systems, e.g., in the Semantic Web, it is necessary to study how to adapt and present such explanations in an understandable way. We report on a series of user studies investigating both entailment explanations via proofs and missing entailment explanations via abduction and counterexamples in the context of Description Logic (DL) ontologies. For the former, we assess the influence of prior knowledge on the necessary explanation granularity; for the latter, we compare the efficacy of abductive versus counterexample-based approaches. While we did not find objectively quantifiable results, we analyse and discuss the results of detailed qualitative user interviews, and extract recommendations for executing user studies on logical reasoning systems.