Some parents offer their school-age children money for each high grade (mark) they get in school.

money As a reward for each high grade at school

Some parents offer their school-age children money for each high grade (mark) they get in school.

An increasing number of people begin to discuss whether it is a good idea for parents to offer their school-age children money for each high grade they get in school, and many people air their opinion based on their own value systems. The majority of people tend to claim that a clear effort-reward system built by parents incentivize their children to study hard and thus cultivate diligence in their whole lifetime. However, does the claim really ring true, conforming to the real situation? I find myself not on the same wavelength with such an idea. It is my contention that using money as reward for high grade will mislead the value systems of children.

There are a bunch of reasons to support my perspective. For starters, holding exams in school is a way not only for children to review what they've learned in a period of time but also for teachers to track the condition of each student. Linking monetary reward with high grade distorts the meaning and purpose of exam, and what's worse, it will misguide some children to do the wrong thing in order to get the money from their parents. For example, the children may cheat during the exam for the questions they forgot to review and still score high and receive the reward. Besides, offering money as a reward indirectly instill the concept into the children that money is the ultimate purpose for doing anything. That is, without money as incentive, the children probably will not pay any effort to achieve better performance in other extracurricular fields such as sport competitions and club presentations.

Although some may claim validity of the argument that sound communications between parents and children about the true meaning of money reward can solve the issues raised above. At first glance, the argument appears to be somewhat convincing, but further reflection reveals that it leaves out some significant factors that should be addressed to substantiate the argument. For children, the attractiveness of money is not from itself, but probably from the toys and snacks that can be purchased using the money. That is, children ultimately will link money reward with toys and gifts, instead of the attitude of diligence. The communication is not persuasive nor powerful as the simple concept directly given by the high-score-and-reward system.

Of course, there may be some people who may disagree with my position on this matter. They may claim that the frequent high grades scored by children are the direct prove of the success of the money reward system. However, I think the reasons I have provided in favor of my point of view are stronger.

I am not good at analysing the mistake of the essay, but I will help you to point out some grammar mistakes

a reward for the high grade
the meaning and purpose of the exam
without money asan incentive
offering money as a reward indirectly instills.....
purpose of doing anything (people will say.....for the purpose of.....)
the validity of the argument
the direct proof of the success (prove is verb, proof is noun. In your case, it is noun)
the monetary reward system (money is noun, monetary is adjective)

The first thing that I want to be clear about is, did you write this as a Task 2 essay test or for some other English exam? You did not include the full instructions for the essay so I am unsure about how to review this essay. It is not a common task 2 essay topic. It would help me offer you better advice if I knew what test you are preparing for. You should also let me know if this is just for a writing exercise. I can't review your content and response due to the lack of instructions, but i can advice you regarding the grammar issues of your paper.

So, aside from the mistakes corrected above, your essay still has several errors in it. I'll discuss those problems below.

Spelling:
instill - instil (single L)
favor - favour (UK spelling as opposed to American spelling)

Conciseness: Use simpler words that flow better with the essay rather than trying to impress with complicated words or phrases that do not feel natural in the written form.

The majority of - Most
At first glance, the - The
probably from - from
ultimately will - will
appears to be - is
somewhat convincing - convincing

Clarity: Again, the words need to feel like a natural reference
purchased - bought

Contraction: In academic writing, always spell out both words. Never use the casual English shortcuts.
they've - they have
what's - what is

Avoid using overused expressions and casual English phrases:
on the same wavelength - ... in agreement