1. One or more computer storage media having computer-executable instructions embodied thereon that, when executed by a computing device, cause the computing device to perform a method for displaying performance data of a machine-learned model, the method comprising: receiving a plurality of training items that have been processed by the machine-learned model; receiving a plurality of test items that have been processed by the machine-learned model; generating a plurality of training item representations for the plurality of training items, wherein one training item representation corresponds to one training item, and wherein each individual training item representation is visually configured based on a label assigned to a training item corresponding to the individual training item representation, the label indicating whether the corresponding training item belongs to a class; generating a plurality of test item representations for the plurality of test items, wherein one test item representation corresponds to one test item, and wherein each individual test item representation is visually configured based on a label assigned to a test item corresponding to the individual test item representation, the label indicating whether the corresponding test item belongs to the class; providing for display, in an item representation display area, a training item display area that displays the plurality of training item representations, wherein a location of each individual training item representation in a first direction is based on a score assigned to the training item corresponding to the individual training item representation, the score corresponding to a probability, determined by the machine-learned model, that the corresponding training item belongs to the class, and wherein a location of each individual training item representation in a second direction is based on a count of training items associated with one of a plurality of score ranges; and providing for display, in the item representation display area, a test item display area that is visually separated from the training item display area and that displays the plurality of test item representations, wherein a location of each individual test item representation in the first direction is based on a score assigned to the test item corresponding to the individual test item representation, the score corresponding to a probability, determined by the machine-learned model, that the corresponding test item belongs to the class, and wherein a location of each individual test item representation in the second direction is based on a count of test items associated with one of the plurality of score ranges.