A TV show or movie can be educational if you choose the right show or depending on what you are interested in. If you go on a cooking channel it shows you how to cook. That is a life skill that can easily be wasted if you never try. And then how are you going to feed yourself.Other shows similar to National Geographic show nature that you might have not even have known till after you watched that one show. There is PBS to help young children to grow. And learn words faster.
Cooking shows can teach people recipes and methods of cooking. Shows which associate being fit can show people what a good diet is and what not to eat and most importantly how to stay in shape. Quiz shows such as "The Chase" can give people a higher knowledge and personal IQ.
Yes, television can be very educational. If you have programs that teach kids about sharing, reading, writing, or math than it becomes educational. Cooking and exercise shows are also educational for adults. Educational programs though don't bring in the big money advertisers or get large viewing so they are typially left off of television.
Television is a commercial medium designed to entertain the masses. Television networks create programs in order to sell advertising time. Education and Television have entirely different goals. Although some video and movie programs may have educational value, as an industry, television can never be a successful means of education students.