Most students do not go on to become scientists and for these students the main goal of science education should be to teach rigorous, evidence-based thinking and to convey a sense of wonder about the natural world. These goals can be met by any branch of science; there is no obvious reason why biology would be better than physics or Earth science would be more important than chemistry. Indeed, it is undoubtedly possible to point to curriculums and classes in all areas of science that do a wonderful job of teaching scientific thought. However, that doesn't mean that it is equally easy for teachers to meet these goals in every domain.
It is clearly important for students to have real, meaningful laboratory experiences in science classes. It is possible to have great labs in all branches of science but the challenges can be quite different. One of the big challenges in biology is that experiments often take an extended period of time. Frequently, getting results is simply not possible in a single, 45 minute class period. Even with 1.5 hour double periods, designing biology experiments that fit can be difficult. On the other hand, working with animals (and even plants, fungus, and protists) is inherently motivating and exciting for most students. Furthermore, many of the most important ideas in biology are less abstract and mathematical than the big ideas in physics and chemistry, and are therefore easier for many students to absorb.
In contrast, physics labs often get much quicker results than biology labs and can have the advantage of being visually dramatic. The difficulty for physics teachers is bridging the gap between the labs and the principles which they demonstrate. It's no secret that physics involves quite a bit of math and many students get so caught up in their struggles with the math that they are unable to see the ideas behind the formulas. One of the most successful solutions to this difficulty is conceptual physics classes, which are often successful in helping students understand the big ideas of physics.
Chemistry labs also tend to be quick enough to fit into class periods and they are often very exciting. Indeed, the most common request I get as a science teacher is for "explosions" which are almost entirely the domain of chemistry. With chemistry labs, the duel challenges are safety and connecting the macroscopic results with the microscopic reasons behind the results. Safety in chemistry labs is often best addressed by having well-designed, dedicated lab rooms in schools. When that is not possible, work-arounds using household chemicals instead of their more exciting and dangerous counterparts are sometimes possible. Connecting lab results with the actions of molecules is becoming easier for teachers as better and better computer simulations for chemistry education are developed.
Earth science is the fourth major branch of science and it is the most forgotten one. In some ways it is the broadest of the subjects; any study of earth science will inevitably touch on aspects of chemistry, physics, and biology. Designing earth science labs is quite challenging because it is impossible to actually manipulate landforms or weather in the classroom. For this reason, earth science labs rely strongly on models. Reliance on models can be a strength if it is used as an opportunity to really explore the place of models in science or it can be a weakness if simple models are used as stand-ins for complex systems without discussion.
Each branch of science has its own advantages and disadvantages from the point of view of a teacher designing a curriculum with a strong, relevant, and exciting laboratory component. For most students, it is not especially important which branch (or branches) that they study; rather it is important that they learn scientific thinking and evidence-based reasoning.
