Something that can be challenging when ​describing complex tasks to developers is knowing whether they really understand all the requirements.

​To some degree, this is just part of normal human interaction and knowledge transfer but there are some ways you can make it less painful.

F​ocus on the outcome
​​When writing up a task, define the conditions and behaviours you will be testing for.In other words, rather than trying to describe the whole solution, you're defining the 'acceptance criteria'.
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​Let them define the milestones
​This forces them to think the whole thing through in order to break the task up into consecutive sections that have a logical order.

​Have them commit to a demo​ for each milestone​
​If they can show the current progress, again this makes sure they understand how the process should work. It also allows you to check for deviance from the requirements as early as possible.

​A lot of the time, technical skills have nothing to do with the productivity of a dev team.

​This kind of approach requires more rigour and negotiation up front, but pays off in the long run and avoids surprises!