We present spectroscopy of two clusters in the dwarf irregular galaxy NGC 6822 .
From these we deduce an age for Cluster VII of 11 ^ { +4 } _ { -3 } Gyr and [ Fe/H ] = -1.95 \pm 0.15 dex .
Cluster VII appears to be an analog of the metal-poor galactic globular clusters .
Cluster VI is found to be much younger and more metal rich , with an age of approximately 2 Gyr .
Its derived metallicity , [ Fe/H ] \approx - 1.0 dex , is comparable to that of the gas seen today in NGC 6822 .
The existence of a metal-poor old cluster in NGC 6822 rules out models for the chemical evolution of this galaxy with significant prompt initial enhancement .
We find that a star formation rate which is constant with time and is within a factor of two of the present star formation rate can reproduce the two points on the age-metallicity relationship for NGC 6822 over the past 10 Gyr defined by these two clusters .