Green’s Dictionary of Slang

(US campus) an academically successful student.

1996

(con. 1930s–40s) Eble Sl. and Sociability 16: However, loss of referent cannot explain the demise of these American college slang terms of the 1930s and 1940s: [...] d.a.r. (from damned average raiser, with the added allusion to the Daughters of the American Revolution) for a ‘student who gets good grades’.