If the trumpet is for an elementary school student who is playing in the band, a beginner should stick with a Bb trumpet. Most elementary school music teachers use method books that encompass all the instruments as parts of a greater whole. These books assume the beginner is playing a Bb trumpet, so choosing a C trumpet would unnecessarily complicate learning in that situation. If the beginner is older, is not part of the school band, or is more interested in orchestral music, a C trumpet is fine.