[DonRotolo]

Jiust like at work: Set clear performance standards for each person, and enforce them. Write down exactly what is expected using "SMART" and modify it until both sides agree. Then, when a standard is not met, you take action. (1st case, verbal warning. 2nd, written. 3rd, off the team).

Seems harsh, but this is how the real world works. Have a mentor be the 'enforcer'.

SMART:
Specific
Measureable
Achievable
Relevant
Time-bound

Specific – Objectives should be as specific as possible, defining what is to be done and by when. The more specific and concrete an objective, the less likely is the potential for misinterpretation.
 Vague: Build drivetrain
 Specific: Design and build a working drivetrain that meets design objectives by the end of Week 3.

Measurable - All objectives should be measurable – that is, well-written objectives need to have some measure and tracking source to determine if they have been achieved. Types of measures include quantities, costs, timeliness, and/or quality.

(Building a drivetrain is not measurable. Buildoing one that works as expected or needed is. "Able to climb hump in 3 seconds" might be one measurable objective)

Attainable but Challenging – Objectives should be realistic and capable of being achieved. Unrealistic expectations are ultimately demotivating, as are objectives that fall outside of an individual’s scope of responsibility. It is also important that objectives be challenging to keep individual’s engaged and motivated.
 Unattainable: Build a drivetrain weighing under 20 pounds, able to climb hump in 1 second and traverse length of field within 4 seconds.
 Attainable: Build a drivetrain weighing under 60 pounds that can climb a hump in 3 seconds and travel at a 12 ft/sec.
(In other words, don't set anyone up for failure. Goals must be within their capabilities and cannot rely on the availability of materials, equipment, etc that is not in their own personal control. A goal of "show up for every meeting" is not good - what if they break their leg, they fail?)

Relevant – Objectives should be relevant to the team's vision and business/strategic objectives, subteam objectives and individual development needs. (A Goal of "show up for every meeting" is nice, but is it relevant?)

Time bound – Objectives need to have a time frame for completion. Deadlines create a sense of commitment and urgency. Of course, deadlines can change depending on unanticipated shifts in priorities, but each objective should have a time by which it is to be completed.
 Not Time bound: Deliver a working drivetrain.
 Time Bound: Deliver a working drivetrain by the end of week 3.

Usually there are several objectives, and generally never as broad as a whole drivetrain. "Design, submit for approval, and fabricate four drivetrain side plates that meet written design and performance objectives by Thursday, January 17" might be appropriate for a mechanical leader perhaps.