Benchmark 5A
The Living Environment: Diversity of Life
Grades 6-8, page 104

For sexually reproducing organisms, a species comprises all organisms that can mate with one another to produce fertile offspring.

NSES Content Standard C 
Life Science: Biological evolution 
Grades 9-12, page 185 
Biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships. Species is the most fundamental unit of classification.