Klar geht das. Beautiful bezeichnet durchaus auch abstrakte Begriffe, siehe zum Beispiel: "A Beautiful Mind".

American Heritage Dictionary
beautiful adj. Having beauty in any of its forms. n. Beauty, as an aesthetic or philosophical principle.
Synonyms: beautiful, lovely, pretty, handsome, comely, fair. All these adjectives apply to that which appeals to the senses or the mind. Beautiful, the most comprehensive, applies to what stirs a heightened response of the senses and of the mind on its highest level. Lovely pertains to that which inspires ardent emotion rather than intellectual appreciation. Pretty suggests only sensory appeal of a limited and superficial nature. Handsome stresses visual appeal by reason of conformity to ideals of form and proportion. Comely is usually restricted to wholesome physical attractiveness. Fair, in this context, emphasizes visual appeal deriving from freshness and purity.

Beautiful poem is (as the words highlighted by bold face above show) is absolutely correct as a translation of "schönes Gedicht". As shown by the list of synonyms above, other words are more strongly linked or limited to physical appearance.

Just a very small selection of the hundreds of thousands of results for "beautiful poetry" or "beautiful poems"... :-)

thanks, everybody. Even if Goldammerson doesn't tell his teacher it will satisfy him personally.