This is a great lesson to emphasize warm and cool colors and simple shapes. I did this lesson with my Kindergartners and my 2nd graders this year. I love this because it is a no-fail lesson with stunning results. We first discussed warm and cool color schemes and painted a horizon line across the middle of the paper. For the water, students were only to use cool paint colors and for the sky, they were only to use warm colors. For the sailboats, I have three stencils on the table that they can trace onto sheets of wallpaper and cut them out. Older students can do this without tracing, but my little ones still need the practice tracing and cutting.
I also utilize this time to teach the students proper use of watercolor paint. I don't know about your students, but mine need several reminders on how to use this art medium correctly. They tend to think that paint needs to be dark and heavy and to achieve the best results, they 'scoop' out the paint instead of dabbing their brush into the paint wells. So, I do a thorough demonstration every time we use watercolors. Now, don't get me wrong, there are always a few students who don't use enough water, use too much paint, or try to mix all of the colors together. And for this student, I breath a big sigh, and remind myself to reteach the watercolor lesson yet again.