Apologia is the gold standard in science curriculum in Christian homeschools. Their resources span elementary school through high school.
We did several of their elementary/middle school studies and loved them! Our favorites included Astronomy, Zoology 2 (Swimming Creatures), and Human Anatomy & Physiology. The textbooks are colorful and easy to follow, and the hands on activities made them perfect for keeping kids (and teachers) interested!
The textbooks are written from a decidedly Christian, young Earth, literal Biblical interpretation perspective. In fact, Dr. Jay Wile, who wrote many of the high school textbooks, was an athiest who changed his views after learning the scientific support for creation. (You can read his story here)
My whole family gives these resources two big thumbs up!