Reserve 4 lemon slices, and set aside. Combine remaining lemon slices, water, tea bags, and gingerroot in a medium saucepan. Bring to a boil; cover, reduce heat, and simmer 5 minutes. Remove from heat, and stir in sugar. Let cool completely; chill at least 1 hour.
Strain tea mixture, discarding tea bags, lemon slices, and gingerroot. Stir in ginger ale. Place ice cubes and reserved lemon slices in 4 glasses; pour tea over ice. Serve immediately.