Estimation is an important skill that we rely on every day for simple tasks, such as providing food for a dinner party or arriving at an appointment on time. Despite its importance, most people have never been formally taught how to estimate. Estimation can also be a vital tool for scientific inquiry. We have created an activity designed to teach children about estimation by relating it to studies using a marine species of grass shrimp that can have hundreds of parasites. To keep the shrimp alive, the parasites have to be estimated quickly so that the animal can be returned to the water. In this activity, children can use basic items such as M&Ms or pennies to learn how to estimate and then they can test their skills. The modifications provided allow teachers to adapt the activity to suit their curriculum. (Contains 3 figures.)