Students use mirrors to practice indirect measurement.
This is more dependable than the traditional shadow activity since it will work on a cloudy day and at any time during the day (you don't have to worry about shadows being too long or too short to measure).
There is a worked out example at the beginning. Students first complete the activity with a short object so that they can measure the item directly in the end and see how close their indirect measurement came to the actual height. Then students will complete the activity for an object too tall or too inconvenient to measure directly. There are diagrams and pictures along the way to guide the activity.
*Note: To complete this activity with your students, you will need approximately one mirror per three students.