The equinox offers a perfect opportunity to explore latitude, longitude, and how the path of Earth around the sun creates seasons. Since my fourth graders already studied the autumnal equinox in September, we will simply review latitude and longitude and watch a five-minute video, The Changing Seasons. If you'd like complete lesson plans, try Tilting Into the Seasons by Deborah Cubillos. Scholastic also offers Internet Resources for Teaching the Vernal Equinox and Science Myth: Can You Balance an Egg on the Spring Equinox?
To see how sunlight is distributed across the globe on the vernal equinox, take a peek at the daylight clock offered by timeanddate.com. My students are mesmerized by this!