By default, your Chromebook will not "automatically connect" to any non-school wifi network you've connected it to.
You will need to update these settings after you've connected to your wifi network.
1. Click in the bottom right hand corner to open the settings.
2. Click on the wifi network you are connected to enter the wifi settings.
3. Click on the name of the network you want to automatically connect to.
4. Toggle the button to "Automatically Connect to this network." It should be blue to indicate you have turned it on.