Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Coastal Guardian (10 points): Fend off the Telmarine ships.
Cair Paravel Custodian (10 points): Rescue Queen Susan's Horn from the throne room.
Gigantic Allies (10 points): Defeat the archers that are threatening Cair Paravel.
Stemming The Telmarine Tide (10 points): Seal the doors and escape Cair Paravel.
A Pyrrhic Victory (35 points): Escape Cair Paravel with Queen Susan's Horn.
Siege Weapon Destruction (10 points): Use the giants to destroy the catapults in Cair Paravel.
Cave Dweller (10 points): Work through the cavern to find a grapple.
Father Christmas' Gifts (10 points): Explore the treasure rooms and find the Pevensie's clothes and gifts.
River Retrieval (10 points): Rescue Trumpkin from the water.
Feral Forest (10 points): Find a safe route through the woods.
Ruins Revealed (35 points): Complete the entire Cair Paravel Ruins area.
Gryphon Flight (10 points): Use gryphons to take out the turret sentries.
Silent Sentries (10 points): Defeat the sentries along the castle walls.
Liberation (10 points): Rescue Cornelius from the dungeons of Miraz's Castle.
Bell Tower Rescue (10 points): Rescue Edmund and Trumpkin from the bell tower.
Surreptitious Arrival (35 points): Complete all of the areas within Miraz's Castle Infiltration.
Small Is Big (10 points): Reach the control room to let the Narnian army in.
Portcullis Peril (10 points): Open the portcullis and let the Narnian army in.
Courtyard Pugilist (10 points): Battle through the courtyard to get to Peter.
Tyrus The Brave (10 points): Reach King Miraz by scaling the castle terraces.
Stable Rescue (10 points): Rescue Cornelius from the stables in Miraz's Castle.
Valiant Escape (35 points): Complete all of the areas in Miraz Castle Assault.
Approach To The How (10 points): Complete the Approach to Aslan's How area.
Lucy's Escape (10 points): Help Lucy escape on horseback from the How.
Smash The Pane (10 points): Defeat the White Witch.
Miraz Vanquished (10 points): Defeat King Miraz in the combat ring.
Defense Of The How (35 points): Successfully complete all areas in and around Aslan's How.
Conqueror Of Lord Gregoire (10 points): Defeat Lord Gregoire in battle.
Into The Cistern (10 points): Find a way into the secret cistern in Aslan's How.
A Cunning Plan! (10 points): Collapse the battlefield by destroying the support pillars.
Conqueror Of Lord Glozelle (10 points): Defeat Lord Glozelle in the Cistern.
Surprise Attack (10 points): Rescue Prince Caspian on the battlefield of Beruna.
Nature's Vengeance (10 points): Take control of the trees and destroy the Telmarine army.
Aslan's Gift (70 points): Rid Narnia of the Telmarines.
Junior Treasure Hunter (10 points): Open 10 bonus chests in single or co-op play.
Treasure Hunter (25 points): Open 25 bonus chests in single or co-op play.
Senior Treasure Hunter (50 points): Open 50 bonus chests in single or co-op play.
Treasure Hunter Extraordinaire (75 points): Open 75 bonus chests in single or co-op play.
Treasure Meister (100 points): Open ALL bonus chests in single or co-op play.
My Body Is A Temple (40 points): Upgrade your health fully in the game.
Find A Friend (15 points): Play 5 missions in co-op play.
Fun With Friends (40 points): Play 15 missions in co-op play.
Caspian's Retribution (20 points): Seek vengeance from 200 Telmarine soldiers.
Girl Power (20 points): Defeat 75 Telmarines as Susan.
Remarkable Rodent (15 points): Defeat 25 enemies as Reepicheep.
Trumpkin's Delight (15 points): Defeat 50 Telmarines as Trumpkin.
Equestrian Antics (10 points): Defeat 20 enemies while on horseback.
Centaur Charge (15 points): Charge around as the centaur and take out 40 Telmarines.
Reply To All (15 points): Issue a reply to 100 Telmarine enemies in the battle.
Salubrious Slumber (10 points): Send 10 guards to sleep with Cornelius' sleep potions.