There can be many reasons to not attend training and some may be good reasons. Whatever the reason the show must go on and we should make best use of group sessions.
What are newcomers afraid of? Hmm... from what I've seen, it's normal for newbies to fell insecure about themselves, especially when the more experienced show their advanced stuff ... No doubt these moves are what newbies want to be able to perform but the problem lies in how to begin?
I feel that the reason behind the 'SHY' attitude is not having a clear guide on how to do things.
It's best to have a leading person, to function as a guide, in a training session. For this, seniors can discuss among themselves on who should guide the group. There's also a good reason to do this. Firstly, newcomers to parkour can learn how to train properly and what they have learned, they can apply it during their individual training. Also, this approach will be much more fun.
Essentially, warm-ups and stretches should be done extensively to avoid injuries. Physical conditioning for strength, power, agility and all those stuff can be included in the 2 hour duration.
After all that, then we can all begin with specific exercises like precisions, vaults, rolls and so on, which is done in repetition. It is by this approach that newcomers can progress much faster and become more comfortable training alongside seniors.
Hence, the role of a guide presents quite a challenge, but nonetheless, will definitely bring good to our nascent community.
Just my 2 sen on the matter guys.