The big error made in teaching the metric system in the USA was that they tried to teach it in the context of converting metric to english units and back again. This is rather difficult to do since there are so many rather random units of measure in the english system. The irony of this was that many of our fathers were in England during WW2 and came back with horror stories about English money which was as chaotic as the system of measures at that time. They couldn't understand why they didn't have a nice logical system like the US. The moral of my rant is that the metric system isn't hard at all, we use it every time we pay for something or make change. Just stop trying to convert back and forth!