I am almost surprised that given your description of his problems in class, that his teacher hasn't suggested testing (hopefully, he is not in a private school). Of course, if he has something like ADD (not ADHD), it is much harder to notice. Yes, you need to find out what is going on. When you know what the problem is then you can start finding ways to solve the problem. Probably a good way to start is to go to this link - http://www.medhelp.org/medical-information/show/2157/Attention-deficit-hyperactivity-disorder-ADHD?page=1#sec_3761
The problem is that this link focus a lot on ADHD. To get a good picture of the whole area, I would suggest buying this book, "The ADD/ ADHD Answer book," by Susan Ashley.
You can go through a school for testing or find a child specialist. I would probably go the pediatric psychiatrist route.
Finally, the only way I know to help a 7 year old mature is to give them time. His tears could come from frustration of his condition. Deal with the condition and the tears will slow down or stop. I should add that crying is also a learned response. If he has always done it, then you cannot expect him stop overnight. If it is something that as started recently, than that is all the more reason to find out what is going on. Good Luck!