Welcome!  Thanks for joining!  

To be honest, I struggled all throughout my schooling and still am.  It takes me a lot more time to complete any assignments than normal.  I accept this and work with it.  People have posted various tips on this site that have worked for them.  Recognizing and limiting triggers, allotting time just for daydreaming, some drugs, finding some creative outlet, and just forcing yourself to get out in the world are some of the tips people have shared.  I'm glad you're confronting this now while he's still young.  If he doesn't learn to manage it soon, it can get a lot worse.  Many people express having problems in school and socializing.  I recommend seeing it in a balanced way, as both a wonderful gift and a challenge.  Ask him if he'd be willing to share some of his daydreams in a story or something.  Encourage his creativity, but do your best to get him engaged when it's not time to daydream.  I'm sorry I don't have any magical cures.  Feel free to post on here asking for advice.  People are often eager to share their experiences.  I wish you luck and applaud your efforts.  

your 7 year old son sounds exactly like me when i was 7.