Mimi, Thanks for sharing this. I'm not sure how the fiddle camps are where you live. The ones I attend are Irish music. The teacher of that "camp" passes out a pile of printed notation that we all first sing to in perfect time. The teacher might explain a little about the tune such as origin, the type of tune it is such as horn pipe, reel, jig, slip jig etc. He also adds a little history about the tune and if there is anything odd or noteworthy about the key signature. Since the camp is mostly about learning new music we are all slogging through them sight reading unless you happened to be lucky enough to know it already. You see a lot of dumbfounded looks at these things sometimes including me :). After about the third time through we begin to get the feel of it and move on to the next. There's generally a pile of at least 20 tunes. The expectation is that we will have learned these well in a few weeks on our own.

The fact that people almost never show up to sessions with printed music means that the expectation is we have them memorized. I might occasionally spot a few players peeking at a small piece of paper tucked in their pocket.

@ABitRusty I can fully relate to thinking I know a tune until I try to play it in a group or play along with one I'm supposed to know. The tunes generally move so fast that if I miss something small the rest are halfway through it before I can attempt to jump back on board. Knowing the players and how they play makes a huge difference. There's a lot of individuality in some of these tunes. 

I love it when I get the "feel" for a song like Mimi mentions. Sometimes I think it should come more naturally. It often doesn't and not everyone plays it with the same kind of vibe. Group playing without music is probably more of a challenge than playing with notation IMHO. The tempo, the dynamics, the individual parts are often more determined by the players than by written music. Players that are used to one another can pick up on things a new player needs to acclimate to.