Unfortunately, the Sun isn't very interesting just now, at solar minimum, without a hydrogen alpha scope. (You might be able to get someone from a local astronomy club to bring such a scope out. My club has done this.) Otherwise, you could certainly attempt a pinhole camera, and see how big you could make the image of the Sun by increasing the distance from the pinhole. See if you could see sunspots without a telescope. Galileo was the first to see sunspots - but he used projection from his then-new telescope.
If there were sunspots to see, using one ocular of a binocular for projected imaging is feasible. Especially with a tripod.
There are other objects that can be seen during the day. These include the Moon and Venus. But i've seen Saturn, and a couple bright stars. You have to know where to look. It helps to have a tracking scope that's aligned. This isn't always something you can arrange.
Very few of the talks given at my astronomy club require observing, and could have been done during the day. One of my talks was a review of free astronomy software. Since there's alot of it, i limited myself to free astronomy software that runs on the free OS, Linux. Club members research and present talks.
You could make 3-D models of the Mars Phobos and Deimos moons. I wish they were in scale with each other. But you could figure out how to make them in scale.
http://www.planetary.org/blog/article/00001348
http://www.planetary.org/blog/article/00001370/
Unfortunately, "High School" doesn't narrow down the audience for me. We had some bright kids in my high school, and some not so bright. And almost no one who was into astronomy. There are plenty of ideas out there, however. Send me mail. Maybe i can point you to some resources.
