Have students arrange a variety of objects in order from shortest to tallest. Cut out shapes or pictures of animals of varying sizes for the activity and have students tape or glue them from shortest to tallest on a piece of paper. Give each student a ruler and show them how to measure each object, explaining that an object that reaches higher on the ruler is taller than another object. Line students up from the shortest to the tallest or you can challenge them to make the line on their own. Talk about what taller students can do that the shorter students cannot and vice versa.
Provide students with a lot of practice classifying objects as the shortest or tallest in a pair. This may be done through a worksheet with simple picture pairs that requires students to circle the shortest object in the pair or write an "S" next to the shortest and "T" next to the tallest. For a hands-on activity, give students two pieces of a candy bar cut to different lengths and ask them to identify the tallest piece. Challenge students by giving them two equal-sized pieces and asking them to make one piece shorter. Many students will figure out that taking a bite out of the candy will make it shorter.
Once students have a basic grasp on the concept, connect it to measurements. Give students rulers and have them measure objects around the room, writing down the measurements. Looking solely at the measurements, help students identify which items are shorter and which items are taller. Write a set of measurements on index cards and tape them to the white board. Have students help group them from shortest to tallest. Measure each student's height, write the numbers on the board and ask students to pick out the shortest student and the tallest student using the measurements.
Online games give students an opportunity to practice the concept of shortest and tallest. PBS Kids' Cyberchase Send in the Trolls game has students choose the correct troll, based on height, to send into space. Eduplace's Compare, Order, and Measure Length interactive provides brief instruction, followed by practice comparing items by length. Topmarks' 3 Bears game has students compare the size of objects to determine what belongs to each of the three bears.