Help students develop an intuition for reliable numerical estimates by filling a jar with pieces of candy, pebbles, marbles or other small objects and letting them guess how many objects are in the jar. To make the activity less haphazard and more educational, use objects of equal size, like marbles. Help students to measure one marble and the size of the jar as the basis for an estimate, or fill a small cup with marbles, count them, and use the information to make an educated guess about the jar.
Create flash cards with various people, animals, buildings and objects on the fronts. Research each item's height, weight, length and age and write these attributes on the back of the cards for the teacher's reference. Draw two or more cards and challenge students to use estimates to order them by a certain attribute. The random combinations will keep the challenges fresh and entertaining as students try, for example, to estimate whether a brontosaurus was taller or shorter than Big Ben, the prominent clock at the north end of the Palace of Westminster.
Estimating total costs is a practical skill that many students can start applying immediately. Create a short menu or price list for a fictional restaurant or store. The prices for items should be non-round numbers, like $5.36 or $2.92. Either let students pick a combination of a few items or assign various combinations and have them estimate the total price in whole dollars. This activity can help start conversations about how people use mathematical skills like estimation in real life.
Bring in photographs of buildings, rivers, crowds or natural formations and assign different values for students to estimate, like the number of workers an office building could accommodate or how many gallons of water flow past a certain point of a river per minute. Have students talk through the assumptions they use to form estimates. An accurate result is not as important as a valid, reasonable approach to each problem is.