I studied at Genki JACS in Tokyo for 3 weeks. Although it's a full-time school (20 hours/week for the standard course), having only 4 hours of school per weekday gives you enough time to study and do some sightseeing depending on your schedule. If you're only staying in Japan for a couple of weeks, but still want to brush up on your Japanese, it's a great deal for the price. They also take care of booking your accommodation; I stayed at a guest house just West of Ikebukuro and it was very convenient for commuting to school and travelling around Tokyo. The classes, which are focused on conversational skills, helped me tremendously and gave me confidence as I interacted with locals! I noticed a difference in my speaking and listening abilities in a matter of days. Overall, this is a great school for those who want to study while travelling.