Student expenditure over a three-year period in the United Kingdom.(practice writing of IELTS Academic Part 1）

The bar graph provides information about that Which category how students who were under 26 and studying in higher/tertiary education used money for from 1996 to 1999 in UK. (it is not from...to but just compares two years - 1996 and 1999)

... categories of expenditure amongst tertiart students in 1986 and 1999

There are eight categories: Accommodation, Food-bills-house hold goods, Essential travel, Non-essential travel, Children, Course expenditure, Entertainment, and Other.

There were common point is It is apparent/clear that the total proportion of expenditure in 1996 and 1999 for of Accommodation, Food-bills-household goods, Entertainment, and Other accounted for/amounted to 80% of whole expenditure.
Also students who were in 1996 and 1999 used the most money for entertainment.

Entertainment expenditure fell from 30 to 25 over the period, but remained as the major item of expenditure

although it decreased slightly in from1996 to 1999, 

The top category stayed steady.

(that is clearly nonsense - how could entertainment exceed accommodation cost!)

In the 3 years period, Essential travel, Entertainment, Other - these 3 categories increased.
Essential travel grow up fell slightly. Entertainment and Other both increased in absolute terms grow almost 5% each from 26% to 32%, and 12% to 16% respectively.
On the other hand, the percentage of the other 5 categories all decreased/declined fell down.
Typically about Expenditure on children , it took up for was 3% in 1996, but no one paied for children nil, or not recorded in 1999.

Overall however, there, However, were little no clearly significant differences, and trends which by category student used money for was were similar between in 1996 and 1999.

Why are you leaving no space before and after numbers: e.g.'3 years'? Also punctuation normally requires a following space. I would have trouble scoring you 5 on this.  Keep working and practising!