Once a week?

Is one hour per week enough for English study?


No.

And this is not a conniving attempt to get people to sign up for more lessons. Both children and adults need to study outside of their English school. When they get home, in the library, or at a cafe with friends- anytime, anywhere. Obviously it is best to talk to foreigners, but if native speakers are not available, there are many other options.

Outside of class you can...

Have a conversation with foreign people (in an English cafe, bar where foreigners frequent, with friends, etc.). You can pick up lots of natural phrases, improve your listening skills, and become more comfortable in a social situation.
Review the text book. Or you'll forget what you learned!
Watch TV/listen to music. In English. There are several English dramas for rent, movies on TV, and music for free online. Find something you enjoy, and it will be very helpful.
Read books/magazines. Pick a topic you love and find a book on it. If the original book is too difficult, try graded readers, such as "Oxford Progressive English Readers." Famous books are simplified and made easy to read. Several levels are available. Manga is useful. Books for adolescents are fun and easier to read as well.
Write. Writing is VERY helpful, especially if you get your teacher to check it. You can learn lots of things that will be useful for future conversations. Also, it's good to actually write down and then see the sentences on paper. For example, write a diary about your daily activities, an essay on current events, or your opinion about a topic important to you. You can learn a lot from your mistakes.

There are several ways to practice and use your English skills outside of the classroom. It's VERY important that you do something. If you take piano lessons, you should practice the piano at home everyday. If you take Karate lessons, you should practice or exercise at home as well. Same with art, cooking, and everything else. Once a week is not enough. 頑張ってね。