One thing that has worked really well for us is to study one or two topics in science per year. For instance, instead of learning a little about habitats one year, and a little more the next, and a little more the next, we just delve right in and learn all about habitats one year and then move on to something totally different the next year.
For instance, this school year we covered habitats for the first half of the year and the human body the second half. We made notebooks for each and included booklets, maps, diagrams, charts, pop-ups, reports, etc. I know these will be brought back out and looked at time and time again.
Studying science this way allows for more time to really expand on a topic and go much more in depth than covering many topics each year. Just skimming the surface of many topics per year may never give the child a real understanding or appreciation for stuying science.
You have the freedom to choose what you'd like to cover and when, especially if your state's homeschooling laws do not require you to test.
These are the topics I have chosen to break our studies into-keep in mind that your topics can and will be different. I've chosen to cover about two per year in order to fit all the topics I want to cover into my "5 year plan".
Habitats and Human Body
Five Kingdoms (This takes all year because I cover insects, plants, etc.)
Astronomy and Geology/Chemistry (I used to just call these two "Earth Science".)
Weather and Recycling/Earth Stewardship
Physics (We do a lot of experiments with this one, so only one topic this year.)
Now, I use a lot of stuff I get from the interenet and a lot of real, living books. Yes, there are actual books to study science beside textbooks! I'm not sure I actually knew that when I was in school! And, it's easier for us to study science twice a week for two hours each, than to try to just do a small amount a day. A smaller amount of time may work for some, but even my younger kids stay interested for at least the first hour to hour and a half. BUT, you can choose what works best for you in that arena, also. That's what makes homeschooing so awesome!