The new Douglas/Gates school does not need sewers. In fact, the new school's on-site septic system was just approved by the Acton Board of Health. Moreover, according to the School Building Committee, the building project cost "is the same if it is sewer (avoided cost) or if it is an independent septic system." That is because the amount that the school would pay in betterment fees is calculated based on the amount that is saved ("avoided") by not having to construct a septic system. So initially, the cost to the school of sewer vs. septic is equal.
However, once the new Douglas/Gates school is hooked up to the sewer, quarterly sewer usage fees would have to be paid out of the school's budget, and sewer usage fees are much higher than annual septic pumping. Therefore, aside from the equal initial cost, sewers represent a higher cost to the school overall.