In a saucepan with a lid, bring 4 cups of water to a boil, and stir in the tapioca pearls (pearls will swell in size). Reduce heat to a simmer, and cook the tapioca until pearls begin to soften, about 7 minutes. Cover the pan, and let the tapioca pearls
stand for 10 to 15 minutes, until the centers are clear. Gently drain the excess water, and set the pearls aside.
Bring 6 cups of water to a boil in a large saucepan and stir in the taro root. Reduce the heat to medium-low, and simmer the taro until soft, about 10 minutes. Add coconut milk and rock sugar, stirring to dissolve the sugar, and simmer for 20 more minutes
to blend the coconut milk and taro. Gently stir in the soft tapioca pearls until well combined. Let cool to room temperature, or serve chilled.