i have heard that boys are slower in the talking skills, my daughter was speaking in sentences by a year but her social skills left a lot to be desired at the time, they all grow at different paces. that being said i do have one idea for you, but i have never had to implement it and i had to be clear on that, because this advice is not derived from experience. you said that he knew the name of things, i was wondering if he points at things and mumbles (as if he wants them), if he does then pretend you are not certain what he is pointing at, and ask him what it is he wants, keep pretending you don't know until he says the word. this next one i do have experience with>> you might try those little flash cards that have texture (like a cat is fuzzy) and a fish has scales), he might combine his auditory, visual, and tactile learning skills and it will be easier, most children are mostly one of those 3 types of student, ask yourself what he has already learned and how it correlates with one of these types, if he mostly identifies with things he is allowed to play with he may be a tactile learner, if he mostly repeats things he hears, then he might be an auditory one, etc... the great thing about the flash cards is that they combine all three