This pattern appears throughout the United States and is caused by systematic assessment regressivity – inexpensive houses are overassessed relative to expensive houses. I use an instrumental variable approach to show that a large portion of this pattern can be attributed to measurement error in sale prices. Sixty percent of the remaining regressivity can be explained by tax assessors’ flawed valuation methods that ignore variation in priced house and neighborhood characteristics and 40% by infrequent reappraisal. A simple valuation method can alleviate assessment regressivity and increase poor homeowners’ net worth by more than 10%.