The chart shows the average class size class in 6 countries

number of students per class - COMPARISON

The bar chart illustrates the comparison between the average number of students per class in six countries and in over the world. Overall, South Korea had a majority of class size, whereas, the proportion of students in Iceland is the lowest in six countries.

Looking at the details, South Korea had the highest percentage of pupils, around 35% is the percentage of 5- to 12-year-old students studying in primary school. This figure was slightly higher than the global average primary's children. It is followed by Japan and Mexico, pupils went to primary school at about 27% and 20% respectively. In the UK and Denmark show similar patterns of use. In both countries, around 21% to 23% of children went to primary school, whereas, Iceland had the least percentage of students, precisely 15%.

On the other hand, South Korea accounted for the highest lower secondary's student in 6 countries and the world, at over 35%. It is followed by Mexico, 33% of 13-to 16-year-old students in lower secondary school. This duration in Japan was a rough increase ( 32%) in the number of students.In UK and Denmark, students went to lower secondary school, at about 22% and 19%, respectively which was lower than the global average. Iceland continues remained the lowest percentage of students in lower secondary school ( approximately 17%).

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The sentence : "Overall, South Korea had a majority ..." should be on another paragraph, then you need to add another overview. writing task 1 in IElts have format: intro+overview+details. It also best if you presen comparisons because I noticed that you just enumerated the details in the graph

Hello!
I like the fact that you have an introduction paragraph before you jump into the bar graph details, but as said in the above comment you have repeated the data in rough figures only but have failed to compare and contrast the same.

I also feel like some word structures, grammar and tense usage is incorrect and would ask you to focus more in these areas as well.

I've done a quick review and will show you some errors that I have noted.

... and in overin over the world averag. Overall, South Korea had holds a majority of inclass size, ... the lowest in among the six countries.

... the global average primary's children of children in primary school.
.., pupils went to attended primary school ...
... show similar patterns of use .

This duration (incorrect word usage - "duration" is not apt) in Japan was ...

You have done a decent job in putting forth this essay. There is much room for improvement though.
Good Luck! :)