This is a great introductory practice for the slipper verbs (verbs with a stem change in the preterite), as it uses a visual aid to help the students understand where the changes are. In addition, it uses the brackets after the verbs that are common in college texts, and has the students reflect on what the brackets mean. Finally, there are reflection questioned designed to prompt understanding about slipper verbs as stem changers with -ir endings.
It is a good first practice for stem changing preterite, and can be used with Realidades 2 or Realidades 3.
See preview for samples.