Abstract: A grammar teaching system maintains and updates a mastery estimate for a grammar skill and displays an updated visual indication of this estimation. Based on user answers to grammar problems, the system updates the mastery estimate for the grammar skill. Also, a step of a grammar problem is associated with an ordered list of hints. When the user requests a hint for the problem step, the system identifies a position in the list of hints based on how many times the user has previously requested hints for the step. The system displays text that is from the hint at the identified position in the list. Further, a hint for a grammar problem step includes pointer information that refers to a portion of a sentence for the grammar problem. When the system displays the hint, the system highlights the portion of the sentence that is referred to in the pointer information.