Here again, we have physics as the primary discipline. Do you think that this is because physics was one of the earliest branches of science developed, is a more readily understandable science early on, or that in retracing scientific advances more people felt it needed to begin with physics? Or, D, none of the above.Physics seems to be the science of choice. I think that physics has been a more 'active' science in the sense that you can really do a lot of experimentation. Physics has grown to include a varied number of studies that were once separate, like magnetism, electricity, light, sound, gravity, mechanics, astronomy, and cosmology (not sure about those last two--probably some usage I'm not familiar with). All of those sciences had been studied without reference to each other for a long time.
Chemistry is a science of experimentation, but it was secret for a very long time. Chemistry is fascinating in what it has done to help us understand atoms, and promote human living. It is a difficult science for home, too, in that to do experiments, even the early ones, probably means a lot of special equipment (beakers, chemicals, vent-hood, safety glasses). Not to mention that early chemistry (if you want to recreate hierarchical experiments) involves a lot of interesting experiments. There was the boiling of urine to find phosphorous, for instance. Early chemistry was also well hidden.
As far as I can tell, not having studied biology except in high school, it is much less of a field for experimentation. It involves a lot of observation. Though one cannot underestimate its importance (genetics, DNA, viruses, etc), it is also difficult to study personally. Slides just aren't that easy to prepare (dry or wet slide, staining, finding specimens). One can purchase a bunch of prepared slides, but that is such a step back from the process that the joy and wonder of discovery become partially divorced from the material.
It seemed to me that chemistry and biology just didn't seem to make as much sense as physics. Now that I know about hierarchy (studying a subject from percepts through to the higher level abstractions like cells and molecules), I'm guessing that had a lot to do with the method of teaching. I wonder, also, if physics has a longer, modern history. I think physic, initially involving the study of motion of bodies, was certainly the easiest to do methodical experiments and observations.
Let's face it, though. Modern physics has subsumed all of the other scientific disciplines. Chemistry at the atomic level is quantum mechanics, along with biology at the subcellular level. Even earth science has physicists investigating the magnetic field.
LB makes a great point. Chemistry, biology and other sciences (earth science, ecology--which I think of as related to biology) are essential to learn. I wonder if they are as easily studied in the younger ages as classical physics. Certainly they have starting points that are easily introduced. Biology would definitely begin with the history of classification.