BPS investor rating slips amid slowed enrollment, COVID-19 Advertisement BIRMINGHAM — After an adjustment to their assessment formula, Moody’s Investors Service has downgraded the Birmingham Public Schools district from an Aa2 to an Aa1 rating. The slip impacts the district’s $213.4 million in outstanding general obligation unlimited tax debt. That’s because the rating reflects the district’s ability to repay debt and obligations. The change in standing might come as a surprise to some, considering that the district serves one of the most affluent cities in the state, which sits in southeastern Michigan, which holds an Aa1 stable rating, and specifically, Oakland County, which has an Aaa stable rating.