1. A recommender system for recommending an educational game to be used by a group of at least two students, the system comprising: at least one tangible processor; and a memory with instructions to be executed by the at least one tangible processor for: receiving a request to recommend an educational game to use with a group of at least two students; accessing student data relating to the at least two students including granular assessment data, wherein the granular assessment data includes a result of at least one assessment administered to respective students of the at least two students, wherein each assessment of the at least one assessment includes a plurality of problems for assessing each of the at least two students and the result includes an independent evaluation of each respective problem of the plurality of problems; associating each of the at least two students with a D-dimensional vector encoding the granular assessment data for that student, the vector including values indicative of an evaluation of each answer to D respective problems, wherein the value for each of the D problems is +1 for a correct answer and −1 for an incorrect answer; determining a similarity of a first student having an associated vector u and a second student having an associated vector v, and applying the formula 0.5*(1+cos(u,v)) to u and v; comparing the similarity of the student data for the at least two students; assigning the at least two students as belonging to one of a homogeneous and heterogeneous group based on the similarity; selecting an educational game from a plurality of educational games, wherein the selecting includes: in response to the at least two students being assigned to the homogeneous group, selecting the educational game based on an average level of mastery for the academic area being exercised for the group, and in response to the at least two students being assigned to the heterogeneous group, selecting the educational game based on various levels of mastery for the academic area being exercised; and, outputting the selected game.