Appropriate grades or age groups:
Grades 5-6

Estimated time to complete this project:
A few minutes to prepare, about a week to observe.

Materials:
3 small annuals (I used marigolds) all about the same size
a box
a lamp
a ruler to measure the plants

Instructions:
I bought 3 marigolds. Each one was in it's own pot. Each plant was measured and documented. Each pot was labeled 1, 2 and 3. Plant 1 got no sunlight, it was placed in a box. Plant 2 got sunlight only during the day. Plant 3 got sunlight all day and lamp light at night. The care of each plant was the same, they were all watered the same amount. At the end of the week the general appearance and size of the plant was documented.

Other comments or suggestions:
This project won my daughter's science fair in her 5th grade year. The key to this is good documentation. It didn't take much effort.