Lesson Six teaches students how to use 4 figure grid references to accurately locate squares on an Ordnance Survey map. Students first learn that 4 figure grid references specify the column then row to identify a whole square from the bottom left corner. They then practice writing grid references for 20 squares on a provided map and play a battleships game with their partner to reinforce using the references. An extension worksheet provides additional exercises to strengthen students' skills with 4 figure grid referencing.