The phrase "a grade below" is correct and usable in written English.
It can be used when comparing levels of achievement or performance, typically in an academic context.
Example: "She received a B on her report card, which is a grade below what she achieved last semester."
Alternatives: "one level lower" or "a step down".
Gov. George W. Bush spoke at a level almost a grade below.
Virtually no college student now gets a grade below a C, just as few grocers rate eggs smaller than "large".
Usually, two of every five students earn a grade below C and must retake the course or change career plans.
Having never seen a grade below "A," I tried not to appear too smug and I actually felt sorry for the classmates she was obviously addressing.
Michael O'Neill's side sought to frustrate and contain Poland but it was obvious within minutes that they were a grade below their opponents.
Today, the Kumuls are made up mainly of players from PNG Hunters who play in the Queensland InTrust Cup, a grade below the NRL.
REPORTER AT LARGE about the Department of Sanitation tests for young men who are trying for "Sanitation Man, Class A," one grade below street-sweeper.
The New Yorker, October 19, 1940 P. 40 REPORTER AT LARGE about the Department of Sanitation tests for young men who are trying for "Sanitation Man, Class A," one grade below street-sweeper.
By John Bainbridge The New Yorker, October 19, 1940 P. 40 REPORTER AT LARGE about the Department of Sanitation tests for young men who are trying for "Sanitation Man, Class A," one grade below street-sweeper.
Would it be wise to prank the kid who'd cry over any grade below an A? Probably not.
To take a near-comic example, the firms did not present a single executive as meriting a pay grade below the 50th percentile of their supposed peer group, according to two people in Feinberg's office.
