An assessment system may present one or more string interaction problems to each of a plurality of students. Students may provide answers to string interaction problems in the form of string edits that, for example, identify deletions, additions, or revisions to a text string of each respective string interaction problem. The assessment system may normalize each string edit by converting each string edit into a student range edit. Each student range edit defines a replacement text string (which could be an empty text string) to be inserted within a range of reference locations relative to an original text string of the string interaction problem (which likewise could be an empty text string). An assessor may associate feedback objects with student range edits that match or, in some embodiments, are within a predetermined distance of an assessor-defined range edit.