Since science, as a subject isn't tested until later, the schools, especially those in danger of failing the unreasonable standards set by NCLB, change their curriculums to focus on the immediate threat. At the elementary level, this has tended to be English.
More than eight hours of instructional time are devoted each week to teaching “English Language Arts” (“ELA” is a story in and of itself) and over five hours per week to math. By comparison, science is taught for less than three hours.In other words, kids are getting short changed in science. They lose their base and by the time emphasis picks up, it's too late. They're uninterested and under prepared.