One thing to keep in mind about the repeated failures of our effort to train Iraqi security forces is that it's always been a bit odd to think of this as a situation where more/better training is actually what's needed. At the end of the day, whatever the shortcomings of our training and equipping mission in Iraq, after all, it's better than anything the Mahdi Army or the domestic Sunni Arab insurgency or AQI or the Badr Organization has. The issue is one of politics, legitimacy, motivation, and leadership.
Muqtada al-Sadr's men aren't well-trained or especially disciplined, but they are fighting for a cause they believe in and that's at least a first step toward creating an effective military force. No American-led training program is going to be able to make up for that kind of shortfall in the political legitimacy of the central government.