This model theorizes that increasing charter school enrollment is having a negative impact on neighborhood schools. Specifically, increasing the concentration of high needs students in these schools which in turn, makes teachers' jobs more difficult and lowers standardized test scores.
A (+) indicates a positive relationship where an increase in one variable necessarily leads to an increase in the next. A (-) indicates an inverse relationship where an increase in one variable necessitates a decrease in the subsequent variable. Thus the model would read that as charter school enrollment increases, neighborhood school enrollment decreases (the inverse would also hold true). However, as the concentration of high needs students in a classroom increases, the demands/pressure on the teacher also increases. This loop can be read in either direction beginning at any starting point.