Since we are not sure of the age or developmental level of your student, we have some general recommendations for you: Preschool Game Little Matchups Opposites and Preschool Game PhotoTouch Opposites by Grasshopper Apps both deal with opposites, including big and small. PhotoTouch is customizable, so that you can load your own photos to teach the big/small concept in a meaningful way with items/objects that are familiar and in the student’s own context. Another suggestion is Park Math HD, where the user has to put animals in order from largest to smallest and vice versa. Big or Small by Sanghoon Lee checks children’s ability to understand the basic concept of size, amount and numbers.