Give each of your students one plastic zipper bag, two cotton balls and a seed. Each student will moisten the cotton balls and will check their water level each day. Have the students seal the bags most of the way and then place them on a counter or window seal that gets adequate light. Try to start the project near the beginning of the semester, so that your students can watch their seeds grow into strong plants. After the root systems develop and the plants begin to form, you can have the students plant them in pots.
You can have your students compare different types of seeds. Not only will they learn that all seeds are different shapes, sizes and colors, but they will identify the rate of seed germination and plant growth. Have the students check their seeds each week and record the amount of growth they see for each of their seeds. Rather than have plants all over your classroom, plant one of each type of seed in your cotton and then transfer them to pots after they are established.
Another variation involves changing environmental factors for your seeds. For each of the factors, plant a separate seed in the cotton balls. Use the same type of seed, though, so that you can truly compare how the factors change the growth rate and plant health. Place one seed in a light place, near a window, and one in a dark location. Keep one seed well watered and allow the other to dry out. Place one seed in an airtight bag with the cotton and leave one open. Have your students identify the differences in the plant growth.
In the first bag, place only the two damp cotton balls with the seed. In the next, place the seed in the cotton balls, and then add a fertile soil. In another bag, plant the seed in the cotton and plant that into one type of mulch. Change the soil or growing medium in each of the bags and include synthetic mulch, sand and any other medium you can think of. Also, use regular dirt, but change one of waters to an acidic pH, one to a base pH and one with a neutral pH. Have the students evaluate the growth.