Whats app - one tick

[Ptarmigan]

When I what's app my son although he's in good signal it only shows one tick. Eventually it goes to two and he gets the message. He has plenty data

[rkelly1]

You can check his speed at Speedtest by Ookla - The Global Broadband Speed Test.

If that isn't an issue and other apps/websites work ok, then you could update or reinstall the app. If reinstalling make sure you back up the chat history in the app settings 

[bristolian]

WhatsApp is an internet-app, EE provide a mobile data connection to the internet.

Is your son able to use other internet-based services on his phone, whilst connected via mobile data? If yes - this is likely to be a problem with the WhatsApp app. If no - your son's problem is the mobile data connection or his phone.