What does the year level improvement score mean in the reports?

Nessy Reading & Spelling lessons and islands are divided by school year, e.g at 4-5 years old, a student is in Reception/Elementary. 

The yearly progression is measured in 10 increments that increase up to Year/Grade 5.9, this is designed as a guideline only and reflects how Nessy matches the national curriculum. A 0.5 yearly progression would be the equivalent of improving by half a year.

The Year level improvement score is the difference between the last two assessments taken, the Previous result compared to the Current result.