GraphQL is a novel query language for implementing service-based software architectures. The language is gaining momentum and it is now used by major software companies, such as Facebook and GitHub. However, we still lack empirical evidence on the real gains achieved by GraphQL, particularly in terms of the effort required to implement queries in this language. Therefore, in this paper we describe a controlled experiment with 22 students (10 undergraduate and 12 graduate), who were asked to implement eight queries for accessing a web service, using GraphQL and REST. Our results show that GraphQL requires less effort to implement remote service queries when compared to REST (9 vs 6 minutes, median times). These gains increase when REST queries include more complex endpoints, with several parameters. Interestingly, GraphQL outperforms REST even among more experienced participants (as is the case of graduate students) and among participants with previous experience in REST, but no previous experience in GraphQL.