Japanese language schools in (or near) shinjuku?

It looks like in December of this year I will be traveling to attend a conference in Tokyo. They just announced that the conference will be in Shinjuku. 

I'm considering splurging and arriving a bit early and attending a language school. Does anyone know of any good language schools in or around Shinjuku?

I will be speaking at the conference. I'm on the fence with whether to go full-ninja-ganbatte and give the talk in Japanese. But regardless of whether I do or not, I still think it would be awesome to arrive early and take some private Japanese lessons.

I can definitely look for this info myself online. I just thought getting some feedback from real people on their experiences might be helpful!
Edited: 2017-09-11, 12:54 pm
I think most of the schools will arrange private lessons. But private lessons will be cheaper if you can coordinate with a person to meet for language class in a cafe. And 100% focused on you.

My friends studied at Nichibei in Yotsuya and liked the emphasis on speaking and listening vs. kanji study; that school was affilitated with Oberlin College. A few other friends liked ARC quite a bit and you will see a lot of comments on the internet about this school. KCP is probably the largest language school in Japan. Kai is smaller and my friends thought it was fine.

Also I sense the language school model has reduced focus on westerners and heavily towards Chinese & Koreans wishing to enroll in Japanese universities or trade schools. But each school seems to have a slightly different bend.

Rates may be significantly lower if you enroll directly via the school vs. a third-party or your local university.
Please for heaven's sake never attend Human Academy-

Terrible method - Students mostly from Uzbekistan and Nepal who just go to Japan to work so they sabotage the class and are disrespectful to the teachers. Sleep in class and constantly mock the teachers in their own language.

I attended in 2016 and was a bad experience.

The worst part is the methodology .... don't waste your money.

Stay away!!!!
I heard a lot of good things about Akamonkai. It might be a slight commute away from Shinjuku. Actually, I'm in the process of writing up a mini guide based off of language school experiences of friends and other users. Will keep you posted.