The four things that actually differ
The work-loading table. Ask every bidder for hours by space type, not a monthly price. A contractor who will not show the hours is hiding the staffing. Two bids at the same price can differ by a full cleaner per building.
The named APPA service level — and whether the hours support it. Naming Level 2 in the narrative and staffing Level 4 in the hours is the single most common defect in custodial bids. It is also contractually enforceable against the contractor once the level is in the scope.
Restrooms, locker rooms and the cafeteria. APPA defines no service level below 2 for restrooms and locker rooms, and its cafeteria figure does not improve from Level 2 through Level 5. These three spaces are around 14% of a school's area but over a third of the nightly hours. A bidder who scaled a Level 2 quote down proportionally to reach "Level 4" is short by 20–25%, and all of it lands in the restrooms.
The wage plan. Turnover in janitorial work is brutal, and a contract priced at the 10th wage percentile will be re-staffed three times in year one. Ask what the crew will be paid and compare it to the local median.
Who is actually bidding
The national firms — ABM, SSC, Aramark, Sodexo, ServiceMaster, Kellermeyer — are built around large portfolios and spread regional management across dozens of buildings, which is why they price large districts well and small ones poorly. Franchise networks compete on price and hand delivery to a unit owner. Regional independents usually give you the best supervision-to-building ratio in the small and mid range.
Questions worth asking every bidder
Who supervises on site, and is that person dedicated to us? What do you pay a cleaner here? How do you cover an unfilled shift? Who clears your staff and how long does it take? Is the summer deep clean in this price or quoted separately? Are consumables included? What happens if you lose staff mid-year?