Learn Italian: Il suo comportamento a scuola era pessimo. - His behavior at school was terrible.

Yes! In Italian, the possessive adjective suo agrees with the gender of the noun being owned (the behavior, il comportamento, which is masculine), not the owner. So il suo comportamento can mean "his behavior" or "her behavior". You have to rely on context to know who it belongs to.

Why is it just "a scuola" and not "alla scuola"?

With certain common everyday places like school (scuola), theater (teatro), and home (casa), Italian uses the preposition a without combining it with "the" (la). So "at school" is always just a scuola.

Why is "era" used for "was" instead of "è stato"?

Era is the imperfect tense of the verb essere (to be). We use the imperfect here because we are describing an ongoing state, a general characteristic, or a situation in the past, rather than a single completed event.

What kind of word is "pessimo", and how does it relate to adjectives like "buono"?