An instrument for measuring the complexity of learning tasks in the field of Law was developed and tested in three experiments. In Experiments 1 and 2, teachers used the card-sort method to rate the complexity of learning tasks. Based on the outcomes, a benchmark scale with four criterion tasks was used in Experiment 3. The results showed the benchmark instrument to be valid and easy to use, allowing instructional designers to design competency-based learning environments that better take task complexity into account. The Instructional Design model, in which teachers determine task complexity, is briefly described.