Each Science A-Z Unit is placed in one of three grade spans (K-2, 3-4, or 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 text complexity: low •, mid ••, and high •••. Lexile® Measures* certified by MetaMetrics® are provided for each Unit Nonfiction Book and FOCUS Book to support the selection of resources for your classroom or individual student needs.
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An approximate correlation chart is available between Science A-Z grade bands / levels and Lexile® Measures. This page also includes additional information about how we determine text complexity. Ultimately, teachers should use their professional judgment to gauge which resources best fit their students.

*Lexile® Measures for texts are certified through a partnership with MetaMetrics®.