Most instrumental music teachers can leave the details to private teachers if a student is advanced enough to think about all these choices. Students in an advanced school music program will probably utilize, at most, a Bb trumpet, Bb flugelhorn, and a C trumpet. Collegiate players may begin to practice on Bb/A or Eb/D piccolo trumpets. For teachers working with professionals in community or church settings, the sky’s the limit to what instruments they may encounter.
Horn. Along with trumpet players, advanced horn players are consistently required to transpose, and orchestral parts in particular may be found in any given key. Unlike trumpet players, horn players usually play on one instrument.* The F/Bb double horn typically fits the needs of players ranging from beginners to professionals. It has two sets of tubing—one in F and one in Bb. The latter tubing is accessed through the use of a thumb valve.
Although an F/Bb double horn has two sets of tubing and, therefore, technically sounds in two keys, players learn fingerings as if the instrument were always pitched in F. What this means in practice is that each pitch can potentially have different fingerings, depending on whether the thumb valve is depressed or not. Players can use this to good advantage for tuning and ease of moving around the instrument, and alternate fingerings even on single tubed instruments are part of playing brass.
*While the F/Bb double horn is quite common, many different horns pitched in different keys exist. Advanced players may choose to play a different horn for various reasons, including instrument weight, sound quality, or historical accuracy. But for the purposes of most teachers, knowledge of the double horn will suffice.
Trombone. Trombonists do not typically need to transpose their parts to play; however, more advanced players commonly encounter parts written in tenor clef. (Likewise, horn players will frequently see bass clef in more advanced literature.)
Like double horns, trombones often have extra sets of tubing that serve to extend the range and increase the ease of certain technical challenges such as fast movements from lower positions to higher positions. The most common attachment for a tenor trombone places the instrument in F—not surprisingly called an F attachment. Players utilize the extra tubing through the use of a trigger. A modern bass trombone will typically have an additional trigger and tubing pitched in Gb, which, when employed with the F attachment, places the instrument in D. Thankfully, we still consider the instrument as a concert pitch instrument, and the player merely needs to learn new positions rather than dealing with transposition during performance.
Tuba. Like trumpets, tubas also come in different keys beyond the typical Bb variety. F tubas and C tubas are common with advanced players and are used for different situations ranging from orchestral playing to chamber music. Unlike trumpet players, tuba players do not typically need to transpose while they play. Rather, they learn new fingerings for each instrument and continue to think in concert pitch.