How to restore to factory defaults

[mavhc]

I'm sending 3 iMacs to a new school, how do I go about wiping them back to factory/latest OS? I had a quick try with the restore from internet option, but it didn't work with a proxy, even if I tried to set it via the terminal.

[furby]

Depending on how you're proxy is setup Apple says it's not supported. OS X: About OS X Recovery - Apple Support

 

Should just be the first method but I'll cover the others for the sake of completeness

 

Hold down "ALT+R" when the mac boots up. (Or just ALT and select Recovery)

Use Disk utility to wipe/format the disk and then reinstall the OS.

 

Or

 

No Recovery Partition;

 

Use DiskMaker X to create a bootable version of OS X

Hold down ALT during boot, choose the USB drive.

Disk Utility - Wipe the disk -> Reinstall OS X

 

Or

 

Add recovery partition - Downloads | Musings

Then same as above, Disk Utility etc.