Final answer:
To say "I used to go to school every day", you should use the form Iba of the verb ir.
Step-by-step explanation:
To say "I used to go to school every day", you should use the form Iba of the verb ir. The verb ir, which means "to go", is an irregular verb in Spanish. The conjugation for the first person singular (yo) in the past tense is iba. So the correct phrase would be "Iba a la escuela todos los días".
Learn more about Conjugation of the verb ir