I hope you don't use 資質差 as the "reason" (or excuse, pardon my being frank) and then do not attempt to find out the real cause. 

Children that have difficulties with maths (especially essay question) is because they do not understand the question.  That is, they don't know how to turn the question into mathematical expression.  If you have the patient to explain them step by step, they will get it sooner or later.

For English, most oriental students have problem because of the lack of exposure, and they are lazy to memorize the spelling. English is the easiest foreign language, at least the grammar is not as complicable as Latin-based language. Do not force the child to memorize individual words, but to get him/her to have interest to read more - subjects that they are interested in.  When we read more, we will pick up those words eventually.  Don't force them to check up dictionary for every word. Tell them to just guess and skip.  Only check when they come across 3-4 times and still don't know then they should check it up.  Just keep the interest to read the story first. 

Language is something you can't grasp without over 20 years of continuous exposure.  As long as the interest and need is there, they will learn it.  Like me, my English marks were terrible in school, but I keep learning after I started working and here I am.  So tell your child, as long as he/she doesn't give up, he/she will be OK.

It's a good learning experience - learn from other's mistakes. They know why it is wrong, where it is wrong, and then when it comes to themselves, it's less likely they will make the same kind of mistake.

That teacher is really a good teacher.  He/she is not just teaching a subject, but teach students a method, a new perspective of life.

將你子女的成績拿來說嘴取笑，情何以堪??

If that really happens, they should be proud of what they become, that they have overcome their difficulties, and they show to others that if you work hard, past records cannot be your obstacle in life.

Just don't understand how come you are so negative.  I always tell people my English was not good, I always got zero marks in school.  My English now is not excellent, but it's OK.  I tried my best and I am able to communicate without problem.  I don't feel shameful about my zero marks, not then, not now.

Maybe not suitable for elementary students,  but for grade 5 and up, this is effective.

1. show to the student, this is not difficult for everybody.  If other can do it, you can.

2. sometimes, students themselves can put things right to the point, (like this one, maths is really depending on if you work hard enough to do the exercises, and then find out why by practice makes perfect.)

My English was never OK in class, but I was lucky to sit for the exam with our top student who briefly told me the way to write my composition and summary, which was simple and clear for me.  I followed the way and I got passed! Sometimes, student-to-student communication is better as they have common language, they are at the same level, and they probably understand what the problem may be from their own studying experience.

雖說A段班不見得認識B段班，但是人生際遇豈能完全掌握，那天你的子女有成就了，卻被成就不高的A段班同學，將你子女的成績拿來說嘴取笑，情何以堪??

當然，這是比較嚴重的說法，通常一笑置之也就罷了，但若要較真來論，也只有是隱私權被侵犯如此而已，畢竟你的子女或是你不見得是什麼大人物，不值得用成績來做為取笑或打擊的工具，而A段班的同學想來也不會為了B段班同學的分數記憶如新，來做為將來人生道路上的舖陳才是。

可能站在家長的立場，感覺被比較了，心裡不舒服。但是數學老師如此處裡還算好，總比不考試不批改試卷好。

事實上，數學科老師的辛苦在於每一題都必須親自改。但百忙中，老師真的能詳閱每一個算式嗎？

這個同學的鼓勵話寫的很好，數學就是要多家練習，是正向的鼓勵喲！同學的鼓勵說不定比家長的鼓勵更有效果。