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A-student; an A student (bookworm); honors pupil; honors student; honours pupil; honours student (cambridge.org); standout; straight-A pupil (Aiduza); valedictorian (mazurov); outstanding student (rechnik); high achiever (grafleonov); excellent pupil; classman; A level student (sponderling; "A levels" in the UK are the exams that confer an advanced qualification (contrasted with "O [ordinary] levels", the exams taken two years earlier) on school-leavers. Just taking or even passing an A level exam does not automatically make you a standout. "An A student" would probably be less ambiguous. Liv Bliss); recipient of award for excellence (Mosley Leigh); A grade pupil; honor student (Речь может быть не только о студенте, но и о школьнике. TranslationHelp)

standout (one who is conspicuous by virtue of excellence or superiority); outstanding worker