First Graders sure do love learning about plants!
The most effective way I have found to teach about plant life cycles is to use lima beans, cotton balls, and zip-lock bags!
It really is so simple-- and they grow quickly!
Put wet cotton balls into your zip-lock bag (you want them wet enough that you can squish out some water, but not so wet that it puddles without pressure.)
Then have your kiddos put 3 or 4 lima beans in the bag (avoid using old beans) :)
Make sure the beans have direct contact with the cotton balls.
I like to tape it to the window, with the beans facing the sun. We take them down to inspect them, but then I always re-adjust the seeds to make sure they face the sun.
I like to do 6-8 extras. That way we can take them out and take a closer look at different stages of growth without risking anyone's precious plant! :) (And it allows for replacing any that mold quickly).
A few things to note:
Not all of them will grow into plants. (Some years I offer the students to trade me for one of the extra bags).
Some will mold-- they can mold really quickly if your kiddos have a lot of germs on their hands.
Some will grow like crazy-- be prepared.
Once the leaves touch the top of the bag- send them home to be replanted. Thy won't live much longer in the bag- they need soil at that point.