Can my son block me from finding him with my find my iphone app?

Can my son block me from locating him with my find my iPhone app? Is there a way for me to know if he has turned it off at all? When I was trying to locate him, he's 15, all I was seeing was a location from 3 hours prior but it showed the real time location of our other phones. Later his phone with location showed up again.

Yes - your son can block sharing of location in several ways.

The best you can do is enforce restrictions on the device to prevent changes to Find My Friend / Location settings, but if your son is savvy enough to know to hide location, they will be savvy enough to:

• google a faraday cage and put the phone in aluminum foil
• enable airplane mode
• powered off the phone
• sign in to an iPad somewhere else and shift that to report their location when they choose

Here's what the restrictions look like and I've heard of good luck just talking over the restrictions with a minor and then agreeing jointly which will help them avoid temptation and which you can graduate them past with trust in the relationship.

At some point you'll need to find another avenue than technical measures for tracking or have an agreement that if you text he has so many minutes to get back to you, etc...

Make sure that in his Find My iPhone settings you have "Send last location" turned on. (Settings > [His Name] > iCloud > Find My iPhone)

That way when his iPhone does go offline, you'll know where he last was. Just make sure that when you change the setting, he doesn't see it.