In inductive learning, the order in which concept instances are presented plays an important role in learning performance. Theories predict that interleaving instances of different con- cepts is especially beneficial if the concepts are highly sim- ilar to each other, whereas blocking instances belonging to the same concept provides an advantage for learning low- similarity concept structures. This leaves open the question of the relative influence of similarity on interleaved versus blocked presentation. To answer this question, we pit within- and between-category similarity effects against each other in a rich categorization task called Physical Bongard Problems. We manipulate the similarity of instances shown temporally close to each other with blocked and interleaved presentation. The results indicate a stronger effect of similarity on interleaving than on blocking. They further show a large benefit of com- paring similar between-category instances on concept learning tasks where the feature dimensions are not known in advance but have to be constructed.