frequent urination in children

Hi ! my son is 4 years old , he frequently urinate ,he goes to the toilet every hour and urinate a normal amount around 100 ml.. even in school his teacher don't allow him to drink untill 2pm..we complained about that. he drinks a glass and half an hour later he has to urinate... and same at night..he looks and acts healthy with a lot of energy.he has been always with that problem, he goes to urinate twice during dinner, should we give him any tests ? thank you.