Children's book including Motor-mouth Marcy, Asian immigrant who made MC's Christmas present, and hypnosis for basketball

Question

There is a book my 3rd/4th grade teacher read to the class in the late '80's that I have been wondering about for years. It's possible that I'm combining multiple books in my head, but assuming that they are all from the same book, highlights include:

1. the character Motor-Mouth Marcy, about whom I remember nothing besides her name (and the assumption that it meant she talked a lot) - I would have thought this would be enough to find the book in a Google search, but it never seems to work
2. a new foreign student who from an Asian country that I think was Vietnam, but I could be mistaken about the specific country; before coming to America, he worked in a factory making toy trains (or some other toy, but I'm pretty sure it was trains), and was excited to discover his maker's mark on the train the main character gets for Christmas. Not a foreign exchange student; his family was also there, since he discussed the mark with them before telling the main character why they were so excited.
3. a "genius" student who hypnotizes the main character to be really good at basketball, and also at one point subdues a bully with a pressure point in his elbow
4. some kind of scene that takes place on a snow sled, and that's all I remember about that scene, except that it was memorable enough to.... umm, remember? Possibly multiple people on a sled that went out of control.

Answer 1

This is probably Satch and the Motormouth by Karen Sommer, published 1987.

I found it by searching the web for school novel "motormouth" snow sled basketball. The first result was this page (a 500-page pdf), where I searched for "motormouth" and found this:

Sommer, Karen. Satch and the Motormouth. David C. Cook/Chariot Books, 1981. ISBN 1-55513-063-1.

Satch, a sixth grader, thinks he has only one problem Motor-mouth Marcie Cook. Why must he sit by. her? Why do they always end up in the same groups? He thinks Marcie is responsible for the anonymous valentines he's getting. He has to rethink this relationship after he learns some startling news about her mother and his father.

I couldn't find the full text of the book to check for the other details you mentioned in the question, but one of the early chapter titles is "Genius at Work" which might refer to the person mentioned in your 3rd point. Searching the text for Vietnam also seems to confirm your 2nd point. Not sure about the snow sled scene.