The Magicians of Caprona, by Diana Wynne Jones, 2001

In both of the dueling magical families of Caprona, spell-making is taught even to the youngest children. But Tonino, of the Casa Montana, can barely summon a spell. All he's good for is reading and talking to cats. If only he could muster some ability, perhaps he could help the Montanas, and the Petrocchis, their enemies, unravel the mystery of why both families' magic seems to be eroding while the Duke of Caprona does nothing but watch Punch and Judy plays. And who's the strange redhead cousin courting cousin Rosa? Great big Italian warmth envelops this ambitious and successful Chrestomanci-meets-Romeo and Juliet. Recommended.