We are doing our own science here, but ds is just 6. I'm not feeling a whole lot of pressure.
I checked out our state's science standards to get a feel for what the public schools were covering, and I also took a peek at the Core Knowledge Scope and Sequence to see what those folks think ought to be covered. I sort of thought both California and CK were all over the map in terms of science topics. None of the topics seemed to inter-relate well. I figured that as long as I covered the same ground during the elementary years, I would just do my own thing.
We are organizing our science topics by scales and systems. An introduction to space science first (Big Bang, solar system, earth-sun-moon system). Earth science next (mostly just the geology stuff this year, weather for another year). Then biomes and a closer look at biology (living things, seven kingdoms, plant parts and animal classification). Moving on in, we'll also look at the human body systems. Then we're going to detour into the physical sciences - measurement, matter, energy (mostly electricity).
Next year, I'm going to zoom out in scale again. Weather and climate first (after the measurement stuff, we'll get to do a lot weather observations), and we'll revisit biomes from the weather perspective too. A finer look at animal phyla and classes. Then cells and microscope work. Chemistry.
I've been collecting tons of trade books and science activity/experiment books. I'm also creating themed boxes -- some are tools and equipment, others are discovery boxes. I've also been reading teacher-education books about inquiry-based learning. I'm getting some cool ideas that I want to incorporate. We also find it is very easy to "live" science. Science questions come up all the time around here, so we just take detours to investigate a question as it comes it. Science is by FAR our favorite subject.
I'd say that if you were interested in going on your own for science, go for it. Schools are so textbooky that it's pretty easy to do far better. If you want some good science units, I'd check out GEMS from Livermore Hall of Science (awesome, AWESOME units! lots of work, but worth it), stuff from TOPS, and I've heard some good stuff about Real Science, but I don't know how their older grade stuff is.