When the graph, chart or table shows a lot of information, it's difficult to decide what to put in your main 'details' paragraphs.
Here's a method that I often use to help me with this decision: expand on the two points that you made in your 'overview' paragraph.
For example, look at this lesson. We can use the two points in the overview paragraph to guide our decisions about what to put in paragraphs 3 and 4:
Expand on the sentence about school A having higher proportions of children with educational problems. In other words, we can make some easy comparisons between school A and B. Don't worry about changes in the figures or comparing the two years.
Now expand on the sentence about changes i.e. falling percentages in school A and rising figures in school B.
I'll use this technique to write my full answer next week.