Ask your students whether they've ever seen flowers on grasses. You might inspire a fruitful debate.
Fall is a good time to challenge students to explore outside to look for signs of grass flowers. You may first want to reveal that grasses are not pollinated by birds, bees, or other insects, but by the wind. Have students brainstorm some of the likely differences between flowers that need to attract pollinators and those pollinated by wind.
When students find flowering grasses, ask, How do you think the way the flower is made helps the pollen disperse?... the seeds disperse? Use some of the flowering grasses students collect to make dried flower arrangements and/or try planting some of the seeds in the classroom.
As an extension, ask students, Why do you think we don't find grass flowers on our grassy lawns? What do you think would happen if we let a patch of grass grow without mowing it? If you have the opportunity, explore this question by roping off an area of grass to observe and not mow for a time. Students may want to measure and compare the growth rate of the unmown grass to the surrounding grass. With luck, they'll get a firsthand view of grass flowers developing.