And recently, some experts believe that it is better to start the course at primary school rather than secondary school.
If there is "Recently" we should write "have believed", however in this case I think we should not write like that, but omit recently is better, don't you think?
The foundation laid and increase in incentive due to their curiosity is invaluable for their future study on the foreign language. And the negative impacts can be offset by clear subject planning of schools.
Well your conclusion is repeated somehow. I mean you have said:
I still believe its advantages outweigh its disadvantages.
so there is no need to say
So in conclusion, its benefits exceeds its drawbacks and it is desirable for schools to carry out this policy.
And one more thing, maybe your essay is a little bit long. Can you handle this within 40 mins or less? 381 words I have counted :)
Besides these minor mistakes, I think your essay is well-written :) various structures, well-organized ideas, wide range vocab and clearly stated. Love to see more of your essays :) Feel free to say if i'm wrong at some points will you?