You are going to investigate how grasses survive being eaten by cows and sheep, or being cut each week by a mower. This is a summer activity unless you can bring a piece of grass and its roots into the warm classroom in winter.
Choose a piece of grass that you know will not be disturbed.
Using a pair of scissors, cut the grass nearly to the ground.
Paint the remaining grass stems with a waterproof paint. Make sure you paint to the bottom of the grass stems.
Go back in a week or a fortnight's time and see what has happened. Look below the painted area.