When I was forced to teach the younger students I found that giving them loads of small, achievable tasks kept them busy and improved classroom behaviour.
With the older students, once they were broken in, more self learning could be introduced, this gave more opportunity to deal with the ones that were struggling.
Project management is the same.
Set simple tasks achievable tasks that you have the skills to check, find out who does as needed, and give them a bigger job next.
The ones that struggle with the simple stuff need guidance, maybe from one of the better workers, before they can move on to bigger jobs.
Project management generally has (expletive deleted) all to do with technical abilities, more to do with people interacting.
I also use a simple metric when assessing trades (generally was for maintenance work).
If their van has non standard wheels fitted i.e. larger alloys with lower profile tyres, I find they tend to rush a job. They usually drive like (expletive deleted), and park inconsiderately, as well.