The things you mention can be solved by actual supervision (you know, a supervisor doing their job) and old-fashioned time clock.
The issue here is expecting the employee to install a spying app on their personal phone. If it’s that important, they should give the employee a work phone with the app.
As part of the contract a worker would probably drive to a school at 5pm, clean it for a few hours, drive home.
Some workers probably realised that there was no one actually validating their work, and didn't show up or only 'worked' for a short period of time.
Its unreasonable to provide a work phone which then comes with a lot of corporate overhead and device management, for something which is probably just a temporary contract.
It seems completely reasonable to agree to location tracking as part of these jobs, since it makes the management and supervision process more efficient. Workers can buy cheap Android phones and run them on WiFi if they wish to separate their work device from their personal device.
It sounds all this "efficiency" ends up in the favor of the company and in a way that just seems out of balance.
Also if these cheap Android phones exist and are usable, you’re contradicting yourself when saying it can’t be provided by the employer. They could allow employee to expense the device.