Students get incomplete sentences which they must form into questions.
The student who asks must ask in the tu form, the student who answers must answer in the yo form. However, they then must expand and say who completed the action in order to use the preterit verbs that get stem changes
Pedir/sopa (Pediste la sopa)
No pedi la sopa, pero mi madre pidio la sopa
Students then write who completed the action
(You could also use direct object pronouns here...I didn't require it)