High Schools set up a local chapter of the NHS. There are some minimum national standards, but the specific criteria/implementation are left to each High School. There is always some grade requirement, and it could include a commitment for some “public service”.
At our high school, "candidates must be members of the junior or senior class and
have a weighted GPA average of 93.75 (no rounding). Eligibility for membership shall then
be evaluated according to service, leadership, and character." You also had to commit to a tutoring rotation.
The chapters have to require at least “a cumulative GPA of 85, B, 3.0 on a 4.0 scale”, so that they adapt a “cut-off” that is suitably achievable and selective for their student body.