Each Science A-Z Unit is placed in one of three grade spans (K-2, 3-4, and 5-6), based on the grade at which the topic is taught in most states. Within each unit, the Unit Nonfiction Books and other key reading materials are provided at three levels of difficulty: low •, mid ••, and high •••.
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An approximate correlation chart is available between Science A-Z levels, Reading A-Z levels, and other common leveling systems. This page also includes additional information about our leveling system. Ultimately, teachers should use their professional judgment to gauge which resources best fit their students.