The words "there", "their", and "they're" are homophones. Homophones sound the same, but have different spellings and meanings.
Below is a free visual support handout with written examples (downloadable from TeachersPayTeachers) to help teach your student the differences in this homophone group.
Visuals often benefit many students in their learning processes. You can use this visual support in conjunction to your lesson, or to guide your student through the free practice worksheets below.