Playing melodies on any instrument is a great practice.
It's much more fun to practice the melody first and get used to each instrument, rather than picking up an instrument and immediately joining an ensemble to play an accompaniment part.
The original idea is to have a group of members who have some familiarity with the instrument and can play simple melodies.
For example, even if the first part of a clarinet plays the melody, the second and third parts are often harmony or accompaniment, and it's safe to say that on a tuba, the melody is rarely played in a piece.
If students know the lyrics to a melody, they will play the melody in one breath until the end of the lyrics, so they will learn to breathe in time with it. Also, playing a melody on an instrument as if they were singing is a big goal for any level of instrumentalist. Even if there are no specifications on the sheet music, they will find that you can express yourself more musically by adding natural dynamics to match the melody.
Even a simple melody requires a variety of techniques to play it musically. It is very useful to play melodies to learn it as music, not as a technique.
Apart from that, I think it is a shame that elementary school students practice instruments without knowing famous melodies that have been considered beautiful and sung for decades by many people.
It's not that the children don't know them, it's that the teachers don't teach them. These days, it seems that even many teachers don't know famous songs.
You can play familiar songs that appear in songbooks used at school right away.
Playing student's favorite melodies on their own instrument with piano accompaniment is a fun experience and an important practice.
In general, nursery rhymes are written in a range that is easy for brass instruments such as trumpets, and it is sometimes possible to practice with woodwind instruments by raising or lowering the range one octave.
There is no need to harmonize with other instruments, so create opportunities to play melodies in the range that suits each instrument and listen to each other.
There are many song scores written in treble clef, but you don't often see ones written in bass clef.
On the next page, I have written some well-known melodies and melodies that I would like student to know in bass clef symbols.
Melodys for bass instruments
Playing melodies you remember on an instrument without relying on sheet music is good practice for your ears. It is more interesting to play a melody in various keys than practicing scales in various keys, and you will understand the meaning of tonality (even if only vaguely). It is easy for students with good ears, but some students have difficulty.
If a bell rings while you are practicing, it would be fun to play the same pitch on an instrument. Sometimes, when a bell rings during a school ensemble, I ask the students, "Can you imitate the melody of this bell?", but no one has been able to do it right away yet.
I guess they had never thought about it like that before. I think that if the teachers at that school try the same thing with their students after I leave, they will be able to do it right away.