What the published comparisons show
Beaufort County School District in South Carolina published both figures against the same 4.1 million square feet: contracted service at about $0.149 per square foot per month, against in-house at $0.248 to $0.264 depending on the wage assumed. In-house cost 1.7 to 1.8 times as much.
The district also published why. Benefits ran at 83.9% of salary for district employees against 9.4% for the contractor. That is the arbitrage, and it is most of the gap.
So where does the saving really come from?
Two places, and only one of them is efficiency. The first is the benefits differential above. The second is a service level cut — most outsourced contracts are written and funded at APPA Level 4 while the in-house operation was running closer to Level 2. If you compare a Level 4 contract to a Level 2 in-house operation and call the difference a saving, you have priced a reduction in cleanliness as a productivity gain.
The honest comparison
Ask for both numbers at the same service level. Ask what the contractor will pay the crew and compare it to what you pay yours. Ask what happens to your current staff. Then decide — but decide on a like-for-like basis.
What outsourcing genuinely buys you
Recruiting and turnover become somebody else's problem, and in janitorial that is a real problem. Coverage for unfilled shifts is contractual rather than an overtime scramble. Equipment capital and replacement move off your budget. Specialist summer work comes with crews who do it every week. Those are real, and they are worth naming separately from the payroll arithmetic.
What it costs you
Direct control, institutional memory, and staff who know the building and the children. Districts that outsource badly usually did it on price alone, with no service level in the contract and no inspection regime behind it.