First the schools:
What Meryem says about Address: "To my husband and myself they presented a flexible attitude: you decide what you would like to learn. For example I would like to improve my professional (Turkish) speaking skills, so a special program for me is receiving everyday via e-mail homework exercises, and have one hour coaching sessions per week to go through the exercises. They have a professional office, with all equipment available".
Another option is Tömer (also located in Alsancak) where you can take group language lessons (Turkish, Chinese, English, German, etc.) starting at a beginner's level and up (level 1, 2, 3, etc.). Tömer schools have the same program throughout Turkey, so if you are travelling across the country, you can easily take the first level in Istanbul, the second in Ankara and the third in Izmir (provided there are enough students for each given level at your preferred date). Classes are rather intensive from 9h to 13h every day (4 x 50 minutes with breaks), five days a week, with an exam at the end of each level. This particular course costs $340.-
Another option is of course to take private lessons; here too, prices vary as does the quality of what you will find depending on what you are looking for.
If you wish to share the name and contact details of your teacher (with their permission), or if you are a Turkish language teacher yourself and would like to post your contact details, please feel free to do so by clicking on "comments" at the bottom of this post!