The following are known Action Replay Codes for Harry Potter and the Prisoner of Azkaban on Nintendo Game Boy Advance (GBA).
These codes were also known as GameShark Codes and in most cases will work on both devices.

These codes are for the U.S. version of the game.

Master Code – Must Be On
20ff6b87
6026565a
61c49b87
a233be59

Have All Items/Equipment
064e9e91
6ec0b715

Infinite All Cards
9cd98e06
50d359dd
f74f56d8
94459844

Folio Bruti Complete
3d19e508
b81c2c3e

Harry: Quick Lvl Up
7520484f
150522fc

Harry: Max/Full SP
93e6897e
6710fc74
4dee68fb
8c338e88

Harry: Max/Full MP
1b0a359c
c21d6e78
6813c60b
d817bb2a

Harry: Max Stats
8c4fa87c
ac43a6ae
d1d4f76d
05792b73

Harry: All Spells
b010d9e5
35c4e734

Debug Menu / Test Maps
a432c9f0
5d832ab8
a7e25ef2
f6a528fc

Note: Press AR Button on main menu for the Debug Menu / Test Maps.