Estimating weight is difficult for some children. This is one of the activities that I use to practice estimating weight, finding actual weight, and practicing subtraction skills as welll. Each group of students are given a tub/basket with various items in it. They will estimate the weight, get the actual weight, and then find the difference between their estimate and the actual measurement. Students then write a brief statement about what they learned for each item. The students love this activity!