How is your wireless settings set on the laptops? Are they through a gpo? No third party software, right?
There is definitely a gpo or reg key you can adjust to make sure wifi authentication happens on boot before logon.
Can you make sure the device is not staying connected to Wifi at reboot by monitoring the ap?
If you are using windows authentication for wifi - like 802.1x (user, not computer)- you may have some deeper issues to work out.
Sorry I'm on my mobile or I would do some digging for you, I'm just working off the cuff.
Edit: The GPO I was thinking of was the "wait for network at computer startup before logon".