I’m teaching some one on one English to a 12 year old kid, and his mom wanted me to buy an English text to work from. Does anyone have any suggestions? I’m really totally in the dark…
If someone with more knowledge/experience had already answered your post, I’d have kept my keyboard mouth shut, but since no one has so far, here goes:
Before you get a book, I think you should first ask the kid’s mom how long he’s been studying English, how many days a week, hours a day, etc., gently explaining your reasons for wanting to know, and taking care not to sound like you’re interrogating her. Maybe you should also write down what she says.
[Oops: I’m editing because I forgot something very important:] What does his mom want you to do? Does she want you to improve his speaking? reading? writing? Again, you could very gently ask her so as not to seem to be interrogating her.
[Double oops: I’m also editing because I just saw that it looks as if you’ve already had teaching time with the kid.] If you’ve already spent some time with the kid, take note of whether he can enter into something like a conversation with you. If so, at what level? Can he answer questions beyond, “How old are you?” etc.? Can he discuss things that are in any degree complex or abstract? If something is funny or interesting to him, how freely can he communicate this to you? Can he use the past tense? Regular past, i.e., -ed? Irregular past such as got, ran, etc.? Can he use plurals? Regular plurals, i.e., -s? Irregular such as geese, mice, etc.?
For one example of what a twelve-year-old could conceivably have in the way of English training–and assuming the kid never spent substantial amounts of time in the UK, the US, Oz, NZ, or Canada–suppose the kid spent several years in some kind of immersion kindergarten, or had several years’ worth English instruction by good local teachers in an English-only kindergarten for 10-12 hours a week. Then, suppose when he entered first grade that his parents followed the kindy up by sending him to evening bushiban classes for several hours a week with native speakers or good local teachers teaching him. In that case, depending on the quality of the instruction and a lot of other factors, most of which I’m probably ignorant of, he might be an advanced student. I believe this would be especially so if either or both of the parents were much involved in his English education. (Some parents get very involved, even parents who know almost no English!)
For the other examples, just crank that first example down a notch, then another notch, then another. . . .
So in my opinion, before getting a book, the question that one needs to try to address (not that I know anything like a foolproof way to do it) is, At what level is this kid’s English?
Hope this helps, but if it didn’t, maybe someone else will post something more helpful. Also, I didn’t mean to make it sound like rocket science. I’m sure you’ll do fine no matter what book you use. 
xp+10K
I’ve never tried to teach a private from a texbook without assessing him or her first. That should always be your step one. Ask the parent what they goal is for the child’s English (passing a test for a school, for boosting him in an English class, to prepare him to study abroad, etc). Then assess his reading, writing, speaking, etc abilities. There are plenty of websites out there that have some basic questions and tests for 12-year-olds and ESL students.
My best suggestion for actually purchasing the textbook is to err on the side of being more advanced than the kid’s level and then find something a little more simple if needed than to bore the kid and make the parent think you’re wasting their time and having a book that your student will probably never use because it’s below their level. If you get something above their level, then you can work up to it.