I believe that students learn best when they work together with materials and figure things out on their own. Rather than lecture about how and why things work, I provide activities that help students see for themselves. After (and during) these activities, I lead class discussions to explain how and why and teach vocabulary. Student observations and ideas are the focal point of these discussions.
My students tell me all the time how much they love science. Just last week I had a conversation that went like this,
Student: Ms. N, on last week's progress report, all my grades were As and Bs, except one C. What subject was that, I can't remember?
Me: I'm not sure, let's check and see...
Student: Well, I know it couldn't have been science because I love all the experiments we do in science and I try really hard in that subject!
Me: **smiley face**
This method is called Inquiry-Based Instruction. I use an instructional model called "The 5E Model:"
I've found this model to be so effective, that I use it in most of my non-science instruction, too. It works great in math and language arts.