I am trying to find the correlation between the students' actual ability level and the level of text he/she read.

A portion of my data looks like this:

Student Ability Level Level Read

1 5 4

2 3 4

3 4 4

When I try to do the correlation, it gives me an error. Does it have to do with the fact that the level read is the same for all three students? Is it possible to find a correlation with this data?