This is the rate at which students are progressing within an Oxford Level (i.e. meeting the quiz score ‘move up’ thresholds) compared with expected rates of movement through a level. See Automatic progression for information on threshold metrics and expected rates.
As a teacher, you are able to see an aggregated view of class progress in the ‘arcs’ on the Class report screen. The Progress arc shows the proportion of children who are moving through their level at the expected rate or more quickly.
You can use the detailed Class report view to then see how individual students are progressing.